linux-kernel - Re: [PATCH 23/25] ALSA/dummy: Replace tasklet with softirq hrtimer

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Date:   Thu, 31 Aug 2017 16:26:50 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Takashi Sakamoto <o-takashi@...amocchi.jp>
Cc:     perex@...ex.cz, anna-maria@...utronix.de,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        peterz@...radead.org, mingo@...hat.com, hch@....org,
        keescook@...omium.org, john.stultz@...aro.org, tglx@...utronix.de
Subject: Re: [PATCH 23/25] ALSA/dummy: Replace tasklet with softirq hrtimer

On Thu, 31 Aug 2017 16:21:17 +0200,
Takashi Sakamoto wrote:
> 
> Hi,
> 
> On Aug 31 2017 21:23, Anna-Maria Gleixner wrote:
> > From: Thomas Gleixner <tglx@...utronix.de>
> > 
> > The tasklet is used to defer the execution of snd_pcm_period_elapsed() to
> > the softirq context. Using the CLOCK_MONOTONIC_SOFT base invokes the timer
> > callback in softirq context as well which renders the tasklet useless.
> > 
> > Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> > Signed-off-by: Anna-Maria Gleixner <anna-maria@...utronix.de>
> > Cc: Jaroslav Kysela <perex@...ex.cz>
> > Cc: Takashi Iwai <tiwai@...e.com>
> > Cc: Takashi Sakamoto <o-takashi@...amocchi.jp>
> > Cc: alsa-devel@...a-project.org
> > ---
> >  sound/drivers/dummy.c |   16 +++-------------
> >  1 file changed, 3 insertions(+), 13 deletions(-)
> 
> I prefer this patch as long as this driver can still receive callbacks
> from hrtimer subsystem.
> 
> Reviewed-by: Takashi Sakamoto <o-takashi@...amocchi.jp>
> 
> Unfortunately, I have too poor machine to compile whole kernel now, thus
> didn't do any tests, sorry.
> 
> I note that ALSA pcsp driver uses a combination of hrtimer/tasklet for the
> same purpose. I think we can simplify it, too. Please refer to a patch in
> the end of this message. (But not tested yet for the above reason...)

The pcsp is a bit special.  It's really high frequent irq calls for
controlling the beep on/off, thus offloading the whole isn't good.


thanks,

Takashi