At Wed, 21 May 2008 08:09:17 +0200 (CEST), Jaroslav Kysela wrote:

On Wed, 21 May 2008, Eliot Blennerhassett wrote:

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On Tuesday 20 May 2008 23:21:13 Jaroslav Kysela wrote:

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Hi all,

I finished migration from HG to GIT. All repositories are converted and we have one "new" repository - alsa-kernel.git which is full Linux 2.6 GIT tree. The old HG alsa-kernel repository was renamed to alsa-kmirror

Hi Jaroslav,

can you clarify what one should do to be able to build latest GIT head.

I built alsa-driver with latest Linux 2.6 tree without any problems.

...

Should I expect the following to work? (as it used to work with Hg)

$ git clone git://git.alsa-project.org/alsa-kmirror.git alsa-kmirror $ git clone git://git.alsa-project.org/alsa-driver.git alsa-driver $ cd alsa-driver $ ALSAKERNELDIR=../alsa-kmirror/ ./gitcompile --with-debug=full

It's not required to set ALSAKERNELDIR to ../alsa-kmirror - it's default now.

...

anyway I get this error

CC [M] /home/eliot/src/alsagit/alsa-driver/i2c/other/pt2258.o make[4]: *** No rule to make target `/home/eliot/src/alsagit/alsa-driver/i2c/other/tea575x-tuner.o', needed by `/home/eliot/src/alsagit/alsa-driver/i2c/other/snd-ak4117.o'. Stop.

It seems that we have a problem with this patch:

Author: Takashi Iwai tiwai@suse.de Date: Fri May 2 12:31:51 2008 +0200

[ALSA] fm801 - Fix kconfig dependency mess of fm801-tea575x

FM801-tea575x tuner has a reverse selection to V4L1 and this causes
nasty dependency problems.

The patch simplifies the dependency with a normal
"depends on VIDEO_V4L1".  This decreases the usability but fixes bugs,
yeah.  If any better feature like "requires" is introduced to kbuild
in future, we'll be able to switch it...

Signed-off-by: Takashi Iwai <tiwai@suse.de>

Do you have enabled SND_VIDEO_V4L1 in your kernel's .config?

Also, show configure output and toplevel.config.

Anyway, I'll apply patches including major changes of kconfig parser soon later (after some issues with shared git repo are resolved). Then we'll revise the problem again.

thanks,

Takashi

At Wed, 21 May 2008 14:30:31 +0200, Rene Herman wrote:

On 21-05-08 12:28, Takashi Iwai wrote:

...

Anyway, I'll apply patches including major changes of kconfig parser soon later (after some issues with shared git repo are resolved). Then we'll revise the problem again.

By the way, I've been pulling in the "latest alsa" repo you recently provided an URL for:

$ git remote show sound-2.6

• remote sound-2.6 URL: git://git.kernel.org/pub/scm/linux/kernel/git/tiwai/sound-2.6.git Tracked remote branches master

What's the status of that one now? Should I continue pulling that one or should I switch to the new alsa-kernel GIT repo? I want to pull it into a Linus clone tree...

We are working on this right now. alsa.git is far currently behind my tree.

One problem we hit is about multiple committers and rebase. If you do git-rebase, the commiter information is touched although the sign-off isn't updated. git-rebase looks apparently designed for the single-commiter model.

Once after we sort out this issue, I'll update the whole alsa.git tree to the latest Linus tree, and move all my stuff. Let's see whether it really works.

Meanwhile, I'll keep syncing my tree with alsa.git as a backup, so the above will be working, too.

thanks,

Takashi

On Wed, 21 May 2008, Rene Herman wrote:

...

...

What's the status of that one now? Should I continue pulling that one or should I switch to the new alsa-kernel GIT repo? I want to pull it into a Linus clone tree...

We are working on this right now. alsa.git is far currently behind my tree.

One problem we hit is about multiple committers and rebase. If you do git-rebase, the commiter information is touched although the sign-off isn't updated. git-rebase looks apparently designed for the single-commiter model.

It's "worse" than that; rebasing is designed for a _private_ development model. git-rebase is a very handy tool for people like myself (people without a downstream that is) and it basically enables the quilt model of a stack of patches on top of git but public trees that have people pulling from them should generally not rebase or everyone who _is_ pulling finds a different tree each time.

I don't see big obstacles with this model. You can do changes in your local tree and when 'git pull' fails from the subsystem tree, pull new subsystem tree to a new branch and do rebasing in your local tree, too.

Rebasing can keep the subsystem tree more clean I think. It's only about to settle an appropriate workflow.

Jaroslav

----- Jaroslav Kysela perex@perex.cz Linux Kernel Sound Maintainer ALSA Project, Red Hat, Inc.

At Wed, 21 May 2008 16:40:37 +0200, Rene Herman wrote:

On 21-05-08 15:48, Jaroslav Kysela wrote:

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On Wed, 21 May 2008, Rene Herman wrote:

...

...

It's "worse" than that; rebasing is designed for a _private_ development model. git-rebase is a very handy tool for people like myself (people without a downstream that is) and it basically enables the quilt model of a stack of patches on top of git but public trees that have people pulling from them should generally not rebase or everyone who _is_ pulling finds a different tree each time.

I don't see big obstacles with this model. You can do changes in your local tree and when 'git pull' fails from the subsystem tree, pull new subsystem tree to a new branch and do rebasing in your local tree, too.

Rebasing can keep the subsystem tree more clean I think. It's only about to settle an appropriate workflow.

I'm also still frequently trying to figure out an/the efficient way of using GIT but it does seem it's not just a matter of "pure downstream" (which I do believe ALSA has few enough of to not make this be a huge problem). For example linux-next is also going to want to pull in ALSA and say it does, finds a trivial conflict with the trivial tree that it also pulls in and fixes things up. If you rebase that which linux-next pulls from I believe it will have to redo the fix next time it pulls from you since it's getting all those new changesets.

I guess this can be avoided by just not rebasing that which linux-next is pulling... and I in fact don't even know if linux-next does any conflict resolution itself, trivial or otherwise.

I thought linux-next does fresh merges at each time, thus it doesn't matter whether a subsystem tree is rebased or not...

Takashi

Hi Rene,

On Wed, 21 May 2008 17:29:56 +0200 Rene Herman rene.herman@keyaccess.nl wrote:

On 21-05-08 16:52, Takashi Iwai wrote:

...

At Wed, 21 May 2008 16:40:37 +0200, Rene Herman wrote:

...

...

I'm also still frequently trying to figure out an/the efficient way of using GIT but it does seem it's not just a matter of "pure downstream" (which I do believe ALSA has few enough of to not make this be a huge problem). For example linux-next is also going to want to pull in ALSA and say it does, finds a trivial conflict with the trivial tree that it also pulls in and fixes things up. If you rebase that which linux-next pulls from I believe it will have to redo the fix next time it pulls from you since it's getting all those new changesets.

I guess this can be avoided by just not rebasing that which linux-next is pulling... and I in fact don't even know if linux-next does any conflict resolution itself, trivial or otherwise.

I thought linux-next does fresh merges at each time, thus it doesn't matter whether a subsystem tree is rebased or not...

Let's ask...

Fresh merges at each release boundary certainly but if it drops/remerges each subsystem when a bug in its for-next branch is found (a supposedly non rare occurence) all the hopefully hundreds or even thousands of linux-next pullers/testers would seem to have to deal with all those completely new merges everytime as well. I'd hope linux-next during a single release would just pull in the one fix (the subsystem's for-linus branch can still fold it in).

Linux-next is rebuilt every day based on Linus' current kernel. I merge all the trees I have been told about and fixup minor conflicts (sometimes reverting commits, sometimes applying patches). So everyday, linux-next is completely new. I do not care if the trees I am merging get rebased.

I have only had a couple of occasions when the merge conflicts were so bad that I had to drop a whole tree, but they were fixed up the next day.

Linux-next has only one downstream - Andrew's mm tree and he bases on a particular day's linux-next tree each time he rebuilds mm. Testers just need to take the complete tree (which isn't too bad if you are using git since all the linux-next trees share a lot of objects).

Does that answer your question?

Hi Rene,

On Thu, 22 May 2008 22:43:04 +0200 Rene Herman rene.herman@keyaccess.nl wrote:

On 22-05-08 03:24, Stephen Rothwell wrote:

...

Linux-next is rebuilt every day based on Linus' current kernel. I merge all the trees I have been told about and fixup minor conflicts (sometimes reverting commits, sometimes applying patches). So everyday, linux-next is completely new. I do not care if the trees I am merging get rebased.

This means you're going to redo all those (same) minor conflict fixups each day again, doesn't it? Or do you pass the fixups back to (one of) the conflicting trees?

I send email about them and most go away after a day or so i.e. something changes to make the conflicts go away. However, the saving grace here is "git rerere" which remembers these conflicts and their resolutions for me so I normally only have to fix them once.

...

Does that answer your question?

But yes, it does, thanks.

OK, good.

On 21-05-08 16:47, Takashi Iwai wrote:

Theoretically we can work only using merges. However, the resultant tree will look too complex with lots of merge points at the time of the next merge window. This is also a nightmare for bisecting. Thus, most subsystem trees do rebase before the merge window in practice, AFAIK.

It'd be appreciated if someone can tell me any good workflow to keep a good-shaped tree without rebasing...

Over here:

http://lkml.org/lkml/2008/5/17/203

Linus suggests to just not do many merges from upstream -- basically only at releases.

I'm only looking at and experiencing things from the limited viewpoint of a leaf node though so I'll shut up for a bit first now as this might not be helpful.

Rene.

On Wed, 21 May 2008, Takashi Iwai wrote:

But, this means that the fixes done outside the subsystem tree cannot be in the subsystem tree itself until the next release. It's a pretty weird situation.

No it is NOT.

Why should you have stuff from outside the subsystem tree?

And quite frankly, the only reason to *need* those fixes in the first place is if you merge random test-kernels during the merge window. What you should strive for is to merge at the stable point, not random kernels to keep you "up-to-date", and suddenly you don't need to make more merges just to get (possibly) new fixes.

See?

If it's the ALSA tree, then what is it doing pulling all the random other stuff that I merge?

In other words - merging my random stuff, THAT is the "weird situation". You should be doing ALSA development, not "random kernel" development.

The method Linus suggested is suitable for random patches like tirival tree, but apparently not for every case.

Umm. Bigger subsystems than ALSA are successfully using it and have no problems, and don't think they need to merge backwards:

[torvalds@woody linux]$ git rev-list v2.6.25.. drivers/net/ | wc -l 739 [torvalds@woody linux]$ git rev-list v2.6.25.. sound/ | wc -l 291

iow, the only reason you seem to think that you need to merge more is that you merged too much, or from a too-unstable base, to begin with.

Aim for basing things on releases, or at least for merging just at stable points (and only when you *need* to, and it will make your life much easier. And the history will automatically be cleaner and less confusing.

Linus

I updated the Developers Zone wiki to reflect the new source repository, making it a little easier to find.

Question: How do we get rss feeds? Is it similar to the HG method? I like being able to monitor the updates via rss, to determine when I need to refresh my tree, as I only really work on the hda-intel stuff at the moment.

Tobin

On Wed, 2008-05-21 at 18:51 +0200, Takashi Iwai wrote:

At Wed, 21 May 2008 09:16:05 -0700 (PDT), Linus Torvalds wrote:

...

On Wed, 21 May 2008, Takashi Iwai wrote:

...

But, this means that the fixes done outside the subsystem tree cannot be in the subsystem tree itself until the next release. It's a pretty weird situation.

No it is NOT.

Why should you have stuff from outside the subsystem tree?

Well, what I meant is about the fixes to the subsystem (say, ALSA) by people in the outside. Not every ALSA-bugfix patch goes into the upstream from ALSA tree. You, Andrew and others pick individually ALSA-fix patches. They will be missing in the ALSA subsystem tree.

And, what if that you need a fix for the fix that isn't in ALSA tree...? IMO, either a rebase or a merge is better than cherry-picks.

...

And quite frankly, the only reason to *need* those fixes in the first place is if you merge random test-kernels during the merge window. What you should strive for is to merge at the stable point, not random kernels to keep you "up-to-date", and suddenly you don't need to make more merges just to get (possibly) new fixes.

See?

If it's the ALSA tree, then what is it doing pulling all the random other stuff that I merge?

In other words - merging my random stuff, THAT is the "weird situation". You should be doing ALSA development, not "random kernel" development.

Hmm, that makes me thinking of the development model. We can leave ALSA tree without upstream fixes as is if user always pull both ALSA and upstream trees. This works for users that are using the latest development kernel.

...

...

The method Linus suggested is suitable for random patches like tirival tree, but apparently not for every case.

Umm. Bigger subsystems than ALSA are successfully using it and have no problems, and don't think they need to merge backwards:

[torvalds@woody linux]$ git rev-list v2.6.25.. drivers/net/ | wc -l 739 [torvalds@woody linux]$ git rev-list v2.6.25.. sound/ | wc -l 291

iow, the only reason you seem to think that you need to merge more is that you merged too much, or from a too-unstable base, to begin with.

Aim for basing things on releases, or at least for merging just at stable points (and only when you *need* to, and it will make your life much easier. And the history will automatically be cleaner and less confusing.

Yes, I see the point.

But, my question is about the divergence between the development and for-linus branches: how to apply patches that exist only in for-linus tree back.

thanks,

Takashi _______________________________________________ Alsa-devel mailing list Alsa-devel@alsa-project.org http://mailman.alsa-project.org/mailman/listinfo/alsa-devel

On 21-05-08 19:07, Tobin Davis wrote:

Question: How do we get rss feeds? Is it similar to the HG method?

There's an RSS button at the bottom of (for example)

http://git.alsa-project.org/?p=alsa-driver.git

Rene.

On Wed, 21 May 2008, Linus Torvalds wrote:

So merging on its own is not "wrong or evil" at all. Merging is a very good operation to do, but *mindless* merging is bad. That's really all that I'm really trying to argue against.

Btw, let me explain this another way.

I do a *lot* of merges as being an "upstream" person. Since 2.6.25, I've done something like 247 merges (and that's not counting the fast-forward ones). If you do

git log v2.6.25.. -author=torvalds

you'll see pretty much just merges. It's simply what I do. I have a few fairly trivial patches every once in a while (although you almost have to add a "--no-merges" to filter out the merges to see them), but doing merges is what I do most.

So why would I tell others to not merge, when I've done several hundred merges in just the last month myself? Isn't that really hypocritical of me?

The symmetry breaking comes from a few things:

- the merges that "upstream" people do are generally smaller, but even when they are large, they have a "theme".

Most merges I do are fairly small, but even when they aren't (eg the network layer merge of all the thousands of commits that were pending for when the merge window opened), they are _directed_.

IOW, when upstream does a merge, it's hopefully (if the process works correctly) going to be about a specific sub-area, even if that area may be pretty big. So the merge has a very specific meaning: "I want to pull in the changes to subsystem 'xyz'"

In contrast, a merge that goes the other way (subsystem merging upstream) generally doesn't get any particular directed development changes, it just gets "everything else".

This also explains why I can do merge summaries, and downstream people generally can not. Look at my merges, and see how they say things like

Merge git://git.kernel.org/pub/scm/linux/kernel/git/sfrench/cifs-2.6

* git://git.kernel.org/pub/scm/linux/kernel/git/sfrench/cifs-2.6: (21 commits) [CIFS] Remove debug statement Fix possible access to undefined memory region. [CIFS] Enable DFS support for Windows query path info [CIFS] Enable DFS support for Unix query path info [CIFS] add missing seq_printf to cifs_show_options for hard mount option ...

iow, when upstream does a merge, it's simply different from when downstream does one - thanks exactly to having a specific purpose.

- I hopefully only merge "release points".

I don't pull from people at random points. I don't pull daily, or even weekly. I pull when a sub-maintainer asks me to pull, and I've tried to teach people to think of their pull requests as literally being "releases" of their tree. Because they effectively are!

No, releases aren't perfect, and there will be bugs, but the same way that I argued that maintainers should generally aim to pull from me mainly at stable release points, I myself want to pull from downstream only when there is _some_ reason to believe that it's a stable point.

So this isn't really a "broken symmetry", but it looks different because subsystem "releases" are smaller and happen more often than a "whole kernel release".

- My tree isn't so much a "development tree" as it is a "integration tree".

IOW, the biggest reason for my tree to exist in the first place is exactly the fact that it gives people a place to go to see what the "union" of the development is. In contrast, the reason people would go to the ALSA tree, or the networking tree, or any of the other specific trees is exactly because they don't want the union, but want to see what's recent in that particular area.

If somebody fetches the tip of the ALSA tree, they may expect sound-related stuff to break, but you'd generally want to make sure that the rest is as stable as possible (while not being _entirely_ stale, of course!)

If somebody fetches my tree, they want it all, and they *expect* to see any breakage (and any new features) that everybody else could have caused.

So the above hopefully explains why I do 350+ merges per release, but still have the gall to tell other people that they shouldn't merge too much.

[ The corrollary to this all is that when downstream does a merge, think about what the merge message can say. How would you descibe the merge?

Can you give a good description of what you merged, and why? That's one thing that merging with releases can give you: you can say "merge with release 'xyz'", and people actually understand the *meaning* of it. Your merge message makes sense - and that implies that the merge itself likely made sense.

If you cannot explain what and why you merged, you probably shouldn't be merging - that's a good rule of thumb right there! Maybe that rule in itself should already be seen as sufficient ]

Linus

On Wed, 21 May 2008, david@lang.hm wrote:

one thing that you have missed in your explination in this thread (although you have made the point in other threads) is that subsystem maintainers have the fear that there are other changes that will interfere with their stuff and want to catch it early.

Yes.

However, that's not just a "my tree" issue. In fact, quite often other trees are more interesting from that angle: for driver subsystems like sound, the changes in Greg's driver core git tree may actually be oftne more relevant and give more of a heads-up than looking at my tree.

per your instructions in prior threads, what they should do is to have a seperate branch on their system that they use as a throw-away branch to pull from your tree, and from their tree to spot problems. As they find problems they can then address them (cherry pick, or whatever)

Yes. Doing throw-away merges is a great way to test not just whether there might be actual merge conflicts, but also to just test that things work together.

And even if you want to concentrate your *development* on just ALSA-specific stuff, you may well want to also test all the changes that have gone upstream from other projects (and often do that _together_ with the changes you have developed yourself). And again, for this kind of testing, doing a throw-away merge to see how it all works together is fine.

so it's not that the ALSA people should only look at your tree at the merge points, it's that they shouldn't pollute their tree that they are going to publish to you with this checking.

Yes. In general, it's a great idea to have "test trees" that aren't really for development, but for testing. That's obviously what 'linux-next' does, but it's something any tester can do (and it doesn't even have to imply any developer skills, although it would generally require at least some comfort with git).

That said, at least as far as I'm concerned, when I pull from some subsystem tree, the thing I really want to know is that the state of that tree is stable on its own. IOW, if the merge itself introduces some subtle bug, that is not only fairly unusual, but it's also something that should not be seen as a bug from the tree I pulled - it's just bad luck.

So a submaintainer should care *most* about the fact that his/her tree is stable on its own. Problems that happen when multiple development trees are merged should be the secondary concern. I'd rather have people test their _own_ code really well, than spending lots of time trying to test every possible combination with other peoples trees.

Linus

At Wed, 21 May 2008 10:43:43 -0700 (PDT), Linus Torvalds wrote:

On Wed, 21 May 2008, Takashi Iwai wrote:

...

Well, what I meant is about the fixes to the subsystem (say, ALSA) by people in the outside. Not every ALSA-bugfix patch goes into the upstream from ALSA tree. You, Andrew and others pick individually ALSA-fix patches. They will be missing in the ALSA subsystem tree.

Well, that's actually fairly rare, but when it happens, either:

• if you didn't get the fix (ie you're are just seeing random patches go in that happen to touch alsa), why should you then merge the WHOLE TREE with all my experimental stuff anyway? You can largely ignore it, knowing it's fixed, and when you ask me to pull, we'll have a good end result.

• if you got the same fix as a patch, just apply it to your tree (ie just ignore what happens upstream). This happens all the time - people duplicate patches simply because two people apply it.

But the real issue is here is that my tree sometimes gets ten THOUSAND commits during the merge window. Do you really want to pull those thousands of commits into your tree just for one or two possible ALSA fixes?

Indeed, that's the whole question. My statement follows in below.

In _my_ tree, at least the people involved with asking me to pull end up also having (a) people test it and (b) aware that it's in my tree, so they work on trying to fix it. But if ALSA just merges at random times, neither of those two cases are true. Nobody will know about or test some random state that ALSA merged into its own tree.

Ask yourself (and ignore the ALSA parts - think of some totally *different* development area) which you think is better

• developing in one area based on a stable base, with the people who do development in that area knowing about that area.

• or develop on top of a churning sea of thousands of changes to other sub-areas that you don't know anything about?

In other words, the reason I ask people to not do lots of merges is more than just "it looks confusing". It's literally a matter of "it's bad development practice". It causes problems. The confusing history is actually *real* - it's not just a "visual artifact" of looking at the result in gitk. The confusing history is a real phenomenon, and implies that people are doing development not based on some tested base.

Yeah, I've been always amazed by gitk graphs :)

...

And, what if that you need a fix for the fix that isn't in ALSA tree...? IMO, either a rebase or a merge is better than cherry-picks.

First off, I don't see why you even need cherry-picks in the first place. I think your argument is bogus, and you're making it because you want to get the end result, not because the argument is valid on its own.

Here, let's see what I committed to the sound subsystem since 2.6.24 (ignoring merges):

git log --no-merges v2.6.24.. --committer=torvalds sound/

and look over that list. Remember: this is not some short timeframe, this is over TWO whole merge windows, ie this is way more commits than we would normally _ever_ get out of sync over.

Realistically, which of those commits aren't (a) either already from you sent to me just as a way to get a quick fix into my tree without merging the whole thing or (b) stuff that can't just be in my tree and doesn't have to be in the ALSA tree until the next release?

Honestly, now: does *any* of those commits look like "we should merge all the other changes just because we need that commit _now_ in ALSA"?

I really doubt it.

Don't get me wrong: I haven't suggested frequent rebases at all. This thread began actually because an update of the present alsa.git tree is required for applying my patches properly. [BACKGROUND: We are trying to make alsa.git tree with multiple committers. And, the current git-rebase doesn't care about sign-offs when a patch was committed by others. But, this is another topic...]

However, I have to point that backport or backmerge is a rare case but does happen certainly.

For example, assume that we now need to change the codes that touch the device creation. Now on the current your tree, the driver core changed the API. So, we need that change as well. However, picking this particular change might not be enough if it's a part of a long series of patches.

BTW, about the stability: we have an independent ALSA tree containing only the subset of the kernel tree (the sound part). On this, we apply patches continuously without rebase or merge. People except for the development kernel testers usually use this tree.

So I'd seriously suggest submaintainers merge *AT*MOST* once a week, and preferably much much less often than that. There simply isn't any real reason to do it more often. Because it can cause problems.

That's why my suggested rule is:

• merge with mainline at major releases

  This is "safe". Yes, releases still have bugs, but on the other hand, they have much fewer problems than random git trees of the day, so they are a lot safer targets to merge.

• merge with mainline if you know there are real conflicts that need to be resolved.

  This isn't "safe", but it's about trying to resolve conflicts early, so at some point the downside of merging with a "random point" is smaller than the downside of delaying the merge!

but perhaps the most important rule is that things should never be *really* black-and-white, and in the end the really fundamental rule should be:

• Use your own judicious good sense, and merge at other points as necessary, but just keep in mind that a merge is a big change.

Yes, merging with git may be technically really really trivial and take all of two seconds of your time, but:

(a) you *do* potentially get thousands of new commits that aren't actually related to your work and that you probably don't know well. (b) others, when they look at your history, will have a harder time following it.

so while I can give you a few guidelines, in the end those guidelines are just _examples_ of when merges can make sense. You need to understand what the impact of a merge is - and that while git makes merging technically pretty damn trivial most of the time, a merge should still be a big deal, and something you think about.

So the kinds of merges I *really* dislike are the ones that are basically "let's do a regular merge every day to keep up-to-date". That's fine if you don't do any development at all and "git pull" is just basically a "track the current development kernel for testing", but if it involves a merge, it means that there is something wrong in your development model.

Oh, this is really helpful. Maybe it should be documented somewhere as a reference...

...

But, my question is about the divergence between the development and for-linus branches: how to apply patches that exist only in for-linus tree back.

How often does it happen? And how big/important are those? I really think it's probably a "maybe once or twice a release cycle".

And then, the actual answer can be different depending on the details. For example, there are really three things you can do:

• ignore it. Is it a cleanup patch (like the sparse patches) or just fairly trivial stuff that doesn't matter in real life ("remove duplicated unlikely()" patch or the /proc fixups)

  This is often the right thing to do. You _will_ merge eventually anyway, we know that. I'd expect merges to happen at least once in the development cycle, maybe twice.

  Yes, the patch may touch the sound system, but do you really _care_ about it happening rigth now, or can you just wait until the next merge you do?

Well, there is another case to think. For example, core API changes or changes of header files. These happen pretty often, at each kernel release, practically :) And, the code I'm working on is for the next kernel release. So, it should follow these changes, too. That is, I need the top-most development tree. This is another "divergence".

Or, I could postpone the changes touching these until the next kernel release -- then the tree gets merged anyhow and patches can be applied safely. But, of course, it means the fix or improvement will be delayed for one kernel release cycle.

• cherry-pick it. Is it a small, simple patch that you want, but that isn't really worth pulling in all the other stuff that you simply don't know?

  This isn't wrong. It shouldn't be *common*, but it's not wrong to have the same patch in two different branches. It makes sense if it is something you really want, but it's still not important or complex enough to actually mege everything else!

Hm, that's what I didn't consider seriously. I thought cherry-picking patches may cause merge errors easily.

• and finally: merge. It really can be the RightThing(tm). Is it a biggish infrastructure change? Is it a series of several related and dependent commits?

  In other words: is it something big enough that you'd rather merge everything else too (which at least has gotten tested together)? If so, merging is absolutely the right thing to do!

So merging on its own is not "wrong or evil" at all. Merging is a very good operation to do, but *mindless* merging is bad. That's really all that I'm really trying to argue against.

If you thought it through, and decided that yes, you really want to merge, then you should merge. I just think a lot of people merge without even thinking about all the other things it involves, just because git made it *so* easy to do.

Yeah, that's exactly what I feel now, too. There is no crystal clear guideline. But, the common sense tells best...

Thanks,

Takashi

At Wed, 21 May 2008 12:02:29 -0700 (PDT), Linus Torvalds wrote:

On Wed, 21 May 2008, Takashi Iwai wrote:

...

...

• cherry-pick it. Is it a small, simple patch that you want, but that isn't really worth pulling in all the other stuff that you simply don't know?

  This isn't wrong. It shouldn't be *common*, but it's not wrong to have the same patch in two different branches. It makes sense if it is something you really want, but it's still not important or complex enough to actually mege everything else!

Hm, that's what I didn't consider seriously. I thought cherry-picking patches may cause merge errors easily.

Cherry-picking can certainly cause merge errors, but not generally very often.

Cherry-picking by definition will obviously apply the *same* patch to two different branches, and as a result, when you merge, that merge will generally be totally clean. So a trivial merge that succeeds without you even noticing is actually the common case.

But you can certainly get merge failures where you then have to fix things up if there were *other* changes to that same area. At that point, you end up with two different branches that changed the same few lines differently, and it doesn't matter if then _some_ of the changes were identical - the fact that others were not is enough to cause a merge conflict.

If cherry-picking is an uncommon situation, the merge problems are not going to show up (and when they do, they'll generally be simple to resolve, especially if you limit cherry-picking to simple fixes). But if you do a *lot* of cherry-picking, and you cherry-pick big changes, then yes, you'll start hitting merge problems.

So cherry-picking is fine if you do it (a) fairly seldom and (b) just to small patches, because then the upsides of cherry-picking (easy to get a single fix without merging everything else) are bigger than the downsides (the potential merge problems later).

IOW, think of cherry-picking as just another tool. It has upsides and downsides. It's not "wrong" per se, but you can use it the wrong way. You shouldn't use a hammer on a screw, and you shouldn't use cherry-picking for big and complex stuff.

Thanks for clarification!

Sounds like I should really do this more often to keep the devel tree clean without merge or rebase.

Takashi

On Wednesday 21 May 2008 18:09:17 you wrote:

It's not required to set ALSAKERNELDIR to ../alsa-kmirror - it's default now.

Without it I get this:

cd alsa-driver/ eliot@zaphod:~/src/alsagit/alsa-driver$ ./gitcompile No alsa-kernel is found. Please specify the correct location via ALSAKERNELDIR environment variable.

Looking at gitcompile script it doesn't mention alsa-kmirror

Meanwhile I will avoid the error by specifying the cards I'm interested in.

-- Eliot

On Fri, 23 May 2008, Ben Stanley wrote:

I get the same problem as Eliot. The procedure $ git clone git://git.alsa-project.org/alsa-kmirror.git alsa-kmirror $ git clone git://git.alsa-project.org/alsa-driver.git alsa-driver $ cd alsa-driver $ ./gitcompile

results in

No alsa-kernel is found. Please specify the correct location via ALSAKERNELDIR environment variable.

Oops. I forgot to modify gitcompile script, too. I only modified Makefile. It's fixed now. Thanks.

Jaroslav

----- Jaroslav Kysela perex@perex.cz Linux Kernel Sound Maintainer ALSA Project, Red Hat, Inc.