From mboxrd@z Thu Jan  1 00:00:00 1970
From: Takashi Iwai <tiwai@suse.de>
Subject: Re: Question on wait_for_avail function
Date: Thu, 06 Jun 2013 08:53:53 +0200
Message-ID: <s5hwqq7rapq.wl%tiwai@suse.de>
References: <1794d77072add642c43309c0a06bfadb.squirrel@www.codeaurora.org>
 <51AF0223.5020901@ladisch.de> <51B02B4B.8080900@codeaurora.org>
Mime-Version: 1.0 (generated by SEMI 1.14.6 - "Maruoka")
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7bit
Return-path: <alsa-devel-bounces@alsa-project.org>
Received: from mx2.suse.de (cantor2.suse.de [195.135.220.15])
 by alsa0.perex.cz (Postfix) with ESMTP id C3E07265516
 for <alsa-devel@alsa-project.org>; Thu,  6 Jun 2013 08:53:19 +0200 (CEST)
In-Reply-To: <51B02B4B.8080900@codeaurora.org>
List-Unsubscribe: <http://mailman.alsa-project.org/mailman/options/alsa-devel>,
 <mailto:alsa-devel-request@alsa-project.org?subject=unsubscribe>
List-Archive: <http://mailman.alsa-project.org/pipermail/alsa-devel/>
List-Post: <mailto:alsa-devel@alsa-project.org>
List-Help: <mailto:alsa-devel-request@alsa-project.org?subject=help>
List-Subscribe: <http://mailman.alsa-project.org/mailman/listinfo/alsa-devel>,
 <mailto:alsa-devel-request@alsa-project.org?subject=subscribe>
Errors-To: alsa-devel-bounces@alsa-project.org
Sender: alsa-devel-bounces@alsa-project.org
To: Patrick Lai <plai@codeaurora.org>
Cc: alsa-devel@alsa-project.org, gsantosh@codeaurora.org, Clemens Ladisch <clemens@ladisch.de>, lgirdwood@gmail.com
List-Id: alsa-devel@alsa-project.org

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:
> >> 2) 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