linux-kernel - Re: [patch 04/11] ALSA: pcsp: Make hrtimer forwarding more robust

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Message-ID: <s5ho88dnkjv.wl-tiwai@suse.de>
Date:   Tue, 28 Sep 2021 10:58:28 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        alsa-devel@...a-project.org, Takashi Iwai <tiwai@...e.com>,
        Jaroslav Kysela <perex@...ex.cz>
Subject: Re: [patch 04/11] ALSA: pcsp: Make hrtimer forwarding more robust

On Thu, 23 Sep 2021 18:04:25 +0200,
Thomas Gleixner wrote:
> 
> The hrtimer callback pcsp_do_timer() prepares rearming of the timer with
> hrtimer_forward(). hrtimer_forward() is intended to provide a mechanism to
> forward the expiry time of the hrtimer by a multiple of the period argument
> so that the expiry time greater than the time provided in the 'now'
> argument.
> 
> pcsp_do_timer() invokes hrtimer_forward() with the current timer expiry
> time as 'now' argument. That's providing a periodic timer expiry, but is
> not really robust when the timer callback is delayed so that the resulting
> new expiry time is already in the past which causes the callback to be
> invoked immediately again. If the timer is delayed then the back to back
> invocation is not really making it better than skipping the missed
> periods. Sound is distorted in any case.
> 
> Use hrtimer_forward_now() which ensures that the next expiry is in the
> future. This prevents hogging the CPU in the timer expiry code and allows
> later on to remove hrtimer_forward() from the public interfaces.
> 
> Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
> Cc: alsa-devel@...a-project.org
> Cc: Takashi Iwai <tiwai@...e.com>
> Cc: Jaroslav Kysela <perex@...ex.cz>

Thanks, applied now to sound git tree.


Takashi