On Mon, 30 Mar 2020 08:51:05 +0200, George Spelvin wrote:
On Mon, Mar 30, 2020 at 08:27:01AM +0200, Takashi Iwai wrote:
On Sun, 29 Mar 2020 20:16:47 +0200, James Bottomley wrote:
We all assume that msecs_to_jiffies is properly optimized so there should be no need to open code it like you're proposing.
Yes, it'd be best if the compiler can handle it properly.
I've tried, and can't figure out how to get the compiler to detect this special case and not invoke the general code. In particular, for a variable x, __builtin_constant_p(x * 1000 % 1000) is false. Even if x is signed and ANSI lets the compiler assume that overflow doesn't happen.
If you can do it, I'm most curious how!
Actually in the very early version of msecs_to_jiffies() was all inlined, so the compiler could optimize such a case, I guess. Now it was factored out to an external function in commit ca42aaf0c861, so it became difficult.
But also I meant to keep using the macro for consistency reason. IIRC, we wanted to eliminate the explicit use of HZ in the past, and it's how many lines have been converted with *_to_jiffies() calls. I don't know whether the eliminate of HZ is still wished, but reverting to the open code is a step backward for that.
Well, you could always add a secs_to_jiffies(x) wrapper. But given that it expands to basically x * HZ, some people might wonder why you're bothering.
Well, comparing with the expanded result doesn't make always sense. With such a logic, you can argue why BIT(x) macro is needed, too. After all, it's a matter of semantics.
I assumed that open-coding x * HZ was the preferred style, so that's what I did.
That's my question, too -- whether the open code is preferred for this particular purpose.
thanks,
Takashi