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From: Takashi Iwai <tiwai@suse.de>
To: "Sridharan, Ranjani" <ranjani.sridharan@intel.com>
Cc: Ranjani Sridharan <ranjani.sridharan@linux.intel.com>,
	Linux-ALSA <alsa-devel@alsa-project.org>,
	Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Subject: Re: [alsa-devel] [PATCH 7/8] ALSA: pcm: Add card sync_irq field
Date: Thu, 21 Nov 2019 22:28:37 +0100
Message-ID: <s5hd0dksyuy.wl-tiwai@suse.de> (raw)
In-Reply-To: <CAFQqKeU4pA_t=veRm0635pZmxpn=C9sNPPUEHkgavynPYxqwFg@mail.gmail.com>

On Thu, 21 Nov 2019 22:17:41 +0100,
Sridharan, Ranjani wrote:
> 
> On Thu, Nov 21, 2019 at 1:13 PM Takashi Iwai <tiwai@suse.de> wrote:
> 
>     On Thu, 21 Nov 2019 21:46:17 +0100,
>     Sridharan, Ranjani wrote:
>     >
>     >     >
>     >     > Hi Takashi,
>     >     >
>     >     > Sorry the stress tests took a while. 
>     >     > As we discussed earlier, adding the sync_stop() op didnt quite
>     help the
>     >     SOF
>     >     > driver in removing the delayed work for snd_pcm_period_elapsed(). 
>     >   
>     >     Yeah, that's understandable.  If the stop operation itself needs
>     some
>     >     serialization, sync_stop() won't influence at all.
>     >   
>     >     However, now after these discussions, I have some concerns in the
>     >     current code:
>     >   
>     >     - The async work started by schedule_work() may be executed
>     >       (literally) immediately.  So if the timing or the serialization
>     >       matters, it doesn't guarantee at all.  The same level of
>     concurrency
>     >       can happen at any time.
>     >   
>     >     - The period_elapsed work might be pending at prepare or other
>     >       operation;
>     >       the async work means also that it doesn't guarantee its execution
>     in
>     >       time, and it might be delayed much, and the PCM core might go to
>     >       prepare or other state even before the work is executed.
>     >   
>     >     The second point can be fixed easily now with sync_stop.  You can
>     just
>     >     put flush_work() in sync_stop in addition to synchronize_irq().
>     >   
>     >     But the first point is still unclear.  More exactly, which operation
>     >     does it conflict?  Does it the playback drain?  Then it might take
>     >     very long (up to seconds) to block the next operation?
>     >
>     > Hi Takashi,
>     >
>     > As I understand the original intention for adding the
>     period_elapsed_work()
>     > was  that snd_pcm_period_elapsed() could cause a STOP trigger while the
>     > current IPC interrupt is still being handled.
>     > In this case, the STOP trigger generates an IPC to the DSP but the host
>     never
>     > misses the IPC response from the DSP because it is still handling the
>     previous
>     > interrupt.
>    
>     OK, that makes sense.  So the issue is that the trigger stop itself
>     requires the ack via the interrupt and it can't be caught because it's
>     being called from the irq handler itself.
>    
>     In that case, though, another solution would be to make the trigger-
>     stop an async work (but conditionally) while processing the normal
>     period_elapsed in the irq handler.  That is, set some flag before
>     calling snd_pcm_period_elapsed(), and in the trigger-stop, check the
>     flag.  If the flag is set, schedule the work and return.  And, you'll
>     sync this async work with sync_stop().  In that way, the period
>     handling is processed without any delay more lightly.
> 
> OK, that makes sense. Thanks for the suggestion.
> Regarding your previous comment about adding flush_work() to the sync_stop()
> op, would that still be required?

Yes, that's needed no matter which way is used; the pending work must
be synced at some point.


Takashi
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  reply index

Thread overview: 38+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-17  8:53 [alsa-devel] [PATCH 0/8] ALSA: pcm: API cleanups and extensions Takashi Iwai
2019-11-17  8:53 ` [alsa-devel] [PATCH 1/8] ALSA: pcm: Introduce managed buffer allocation mode Takashi Iwai
2019-11-18 16:24   ` Pierre-Louis Bossart
2019-11-18 18:46     ` Takashi Iwai
2019-11-17  8:53 ` [alsa-devel] [PATCH 2/8] ALSA: docs: Update for " Takashi Iwai
2019-11-17  8:53 ` [alsa-devel] [PATCH 3/8] ALSA: pcm: Allow NULL ioctl ops Takashi Iwai
2019-11-17  8:53 ` [alsa-devel] [PATCH 4/8] ALSA: docs: Update document about the default PCM " Takashi Iwai
2019-11-17  8:53 ` [alsa-devel] [PATCH 5/8] ALSA: pcm: Move PCM_RUNTIME_CHECK() macro into local header Takashi Iwai
2019-11-17  9:42   ` kbuild test robot
2019-11-17 10:05     ` Takashi Iwai
2019-11-17 10:28   ` kbuild test robot
2019-11-17  8:53 ` [alsa-devel] [PATCH 6/8] ALSA: pcm: Add the support for sync-stop operation Takashi Iwai
2019-11-18 16:33   ` Pierre-Louis Bossart
2019-11-18 18:47     ` Takashi Iwai
2019-11-17  8:53 ` [alsa-devel] [PATCH 7/8] ALSA: pcm: Add card sync_irq field Takashi Iwai
2019-11-18 16:38   ` Pierre-Louis Bossart
2019-11-18 18:52     ` Takashi Iwai
2019-11-18 19:20       ` Sridharan, Ranjani
2019-11-18 19:49         ` Takashi Iwai
2019-11-18 19:55           ` Sridharan, Ranjani
2019-11-18 20:40             ` Takashi Iwai
2019-11-18 23:47               ` Ranjani Sridharan
2019-11-19  6:44                 ` Takashi Iwai
2019-11-19  7:40                   ` Ranjani Sridharan
2019-11-19  8:24                     ` Takashi Iwai
2019-11-19  9:39                       ` Takashi Iwai
2019-11-19 16:36                       ` Ranjani Sridharan
2019-11-19 21:27                         ` Takashi Iwai
2019-11-19 21:43                           ` Sridharan, Ranjani
2019-11-21 19:22                             ` Sridharan, Ranjani
2019-11-21 20:34                               ` Takashi Iwai
2019-11-21 20:46                                 ` Sridharan, Ranjani
2019-11-21 21:13                                   ` Takashi Iwai
2019-11-21 21:17                                     ` Sridharan, Ranjani
2019-11-21 21:28                                       ` Takashi Iwai [this message]
2019-11-21 21:45                                         ` Sridharan, Ranjani
2019-11-22  4:08                                     ` Jie, Yang
2019-11-17  8:53 ` [alsa-devel] [PATCH 8/8] ALSA: docs: Update about the new PCM sync_stop ops Takashi Iwai

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