[alsa-devel] Question on wait_for_avail function
Hi Liam,
Consider an use case 1) Write is blocked as there is no space to write the data, after the return from snd_pcm_playback_avail()function in wait_for_avail 2) HAL issues pause in parallel to the write I see that the following function snd_pcm_post_pause unblock the write wake_up(&runtime->sleep); wake_up(&runtime->tsleep); But i do not see any case handling for the pause state in the wait_for_avail function, it is not coming out of the for loop as there will not be any change in the buffer states.
Please explain what is the intention behind the wake in pause callback.
Want to understand why there is no handling of pause in wait_for_avail function.
and also is there any restriction from ALSA framework that we should not issue pause while write is blocked or going on.
Regards, Santosh M G.
gsantosh@codeaurora.org wrote:
- HAL issues pause in parallel to the write
This is illegal. http://www.alsa-project.org/main/index.php/SMP_Design says: | The use of returned handles [such as snd_pcm_t*] must be serialized in | the application using own locking scheme.
If you want to issue a pause while waiting for data to be written, use non-blocking writes.
Regards, Clemens
+ << Jaroslav >> On 6/5/2013 2:17 AM, Clemens Ladisch wrote:
gsantosh@codeaurora.org wrote:
- HAL issues pause in parallel to the write
This is illegal. http://www.alsa-project.org/main/index.php/SMP_Design says: | The use of returned handles [such as snd_pcm_t*] must be serialized in | the application using own locking scheme.
If you want to issue a pause while waiting for data to be written, use non-blocking writes.
Based on my understanding of SMP_Design and response above, pause and write to same PCM device are expected to be serialized. However, my interpretation of following patch is that pause and stop are expected to wakes up process waiting in pcm_lib.c wait_for_avail(). It seems to give me the indication that multiple threads acting on same PCM device is expected.
ALSA: pcm_core: Fix wake_up() optimization
This change fixes the "ALSA: pcm_lib - optimize wake_up() calls for PCM I/O" commit. New sleeping queue is introduced to separate user space and kernel space wake_ups. runtime->nowake is renamed to twake (transfer wake).
Jaroslav: Can you share your thought as you are author of this patch?
Thanks Patrick
Regards, Clemens _______________________________________________ Alsa-devel mailing list Alsa-devel@alsa-project.org http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
At Wed, 05 Jun 2013 23:25:15 -0700, Patrick Lai wrote:
- << Jaroslav >>
On 6/5/2013 2:17 AM, Clemens Ladisch wrote:
gsantosh@codeaurora.org wrote:
- HAL issues pause in parallel to the write
This is illegal. http://www.alsa-project.org/main/index.php/SMP_Design says: | The use of returned handles [such as snd_pcm_t*] must be serialized in | the application using own locking scheme.
If you want to issue a pause while waiting for data to be written, use non-blocking writes.
Based on my understanding of SMP_Design and response above, pause and write to same PCM device are expected to be serialized. However, my interpretation of following patch is that pause and stop are expected to wakes up process waiting in pcm_lib.c wait_for_avail(). It seems to give me the indication that multiple threads acting on same PCM device is expected.
ALSA: pcm_core: Fix wake_up() optimization
This change fixes the "ALSA: pcm_lib - optimize wake_up() calls for PCM I/O" commit. New sleeping queue is introduced to separate user space and kernel space wake_ups. runtime->nowake is renamed to twake (transfer wake).
Jaroslav: Can you share your thought as you are author of this patch?
I don't understand what's the problem in this thread...
The behavior of PAUSED stream in wait_for_avail() is clear. If it's woken up by some events, it simply goes to sleep again without exiting the loop.
Takashi
At Wed, 05 Jun 2013 23:25:15 -0700, Patrick Lai wrote:
- << Jaroslav >>
On 6/5/2013 2:17 AM, Clemens Ladisch wrote:
gsantosh@codeaurora.org wrote:
- HAL issues pause in parallel to the write
This is illegal. http://www.alsa-project.org/main/index.php/SMP_Design says: | The use of returned handles [such as snd_pcm_t*] must be serialized
in
| the application using own locking scheme.
If you want to issue a pause while waiting for data to be written, use non-blocking writes.
Based on my understanding of SMP_Design and response above, pause and write to same PCM device are expected to be serialized. However, my interpretation of following patch is that pause and stop are expected to wakes up process waiting in pcm_lib.c wait_for_avail(). It seems to give me the indication that multiple threads acting on same PCM device is expected.
ALSA: pcm_core: Fix wake_up() optimization
This change fixes the "ALSA: pcm_lib - optimize wake_up() calls for PCM I/O" commit. New sleeping queue is introduced to separate user space and kernel space wake_ups. runtime->nowake is renamed to twake (transfer wake).
Jaroslav: Can you share your thought as you are author of this patch?
I don't understand what's the problem in this thread...
The behavior of PAUSED stream in wait_for_avail() is clear. If it's woken up by some events, it simply goes to sleep again without exiting the loop.
We are facing the following issue and want to understand how ALSA is implemented pause, prepare and write if used asynchronously.
for the every seek operation we issue pause and prepare, till now in all the system the issue of (pause + prepare) commands and write are serialized. we are trying to decouple the write and other operation (pause and prepare) to issue in commands asynchronously.
Assume the case below, write is blocked in wait_for_avail as there is no space for the buffer, in between user issued seek on the same session this triggers pause and prepare operations.
pause command will unblock the thread blocked in wait_for_avail, this unblocked thread once again check if buffer avail and if buffer is not avail it goes for wait in loop. after the pause operation is done, HAL issues prepare in prepare we reset the buffer but never unblock the thread waiting in the wait_for_avail. this results in write thread blocked forever and it never gets unblocked as a result the session is blocked.
please help us to know why the implementation of the pause and prepare is this way and are we allowed to do the pause, prepare and write in asynchronously on the same session in copy interface.
Takashi _______________________________________________ Alsa-devel mailing list Alsa-devel@alsa-project.org http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
At Thu, 6 Jun 2013 18:29:35 -0000, gsantosh@codeaurora.org wrote:
At Wed, 05 Jun 2013 23:25:15 -0700, Patrick Lai wrote:
- << Jaroslav >>
On 6/5/2013 2:17 AM, Clemens Ladisch wrote:
gsantosh@codeaurora.org wrote:
- HAL issues pause in parallel to the write
This is illegal. http://www.alsa-project.org/main/index.php/SMP_Design says: | The use of returned handles [such as snd_pcm_t*] must be serialized
in
| the application using own locking scheme.
If you want to issue a pause while waiting for data to be written, use non-blocking writes.
Based on my understanding of SMP_Design and response above, pause and write to same PCM device are expected to be serialized. However, my interpretation of following patch is that pause and stop are expected to wakes up process waiting in pcm_lib.c wait_for_avail(). It seems to give me the indication that multiple threads acting on same PCM device is expected.
ALSA: pcm_core: Fix wake_up() optimization
This change fixes the "ALSA: pcm_lib - optimize wake_up() calls for PCM I/O" commit. New sleeping queue is introduced to separate user space and kernel space wake_ups. runtime->nowake is renamed to twake (transfer wake).
Jaroslav: Can you share your thought as you are author of this patch?
I don't understand what's the problem in this thread...
The behavior of PAUSED stream in wait_for_avail() is clear. If it's woken up by some events, it simply goes to sleep again without exiting the loop.
We are facing the following issue and want to understand how ALSA is implemented pause, prepare and write if used asynchronously.
for the every seek operation we issue pause and prepare, till now in all the system the issue of (pause + prepare) commands and write are serialized. we are trying to decouple the write and other operation (pause and prepare) to issue in commands asynchronously.
Assume the case below, write is blocked in wait_for_avail as there is no space for the buffer, in between user issued seek on the same session this triggers pause and prepare operations.
pause command will unblock the thread blocked in wait_for_avail, this unblocked thread once again check if buffer avail and if buffer is not avail it goes for wait in loop. after the pause operation is done, HAL issues prepare in prepare we reset the buffer but never unblock the thread waiting in the wait_for_avail. this results in write thread blocked forever and it never gets unblocked as a result the session is blocked.
What do you mean "prepare" in the context above? Moving to SND_PCM_STATE_PREPARE? If so, you can't. For preparing the stream, you must stop the stream once. So, you have to issue snd_pcm_drop(), so that stream goes to SND_PCM_STATE_SETUP, then you can do prepare, and restart.
In other words, from the PAUSED state, it can change to only either RUNNING (via PAUSE_RESUME trigger) or SETUP (via snd_pcm_drop) state. (There are other possible states like DRAINING, SUSPENDED or DISCONNECTED, but let's ignore now. )
Takashi
please help us to know why the implementation of the pause and prepare is this way and are we allowed to do the pause, prepare and write in asynchronously on the same session in copy interface.
Takashi _______________________________________________ Alsa-devel mailing list Alsa-devel@alsa-project.org http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
Alsa-devel mailing list Alsa-devel@alsa-project.org http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
participants (4)
-
Clemens Ladisch -
gsantosh＠codeaurora.org -
Patrick Lai -
Takashi Iwai