Re: [Qemu-devel] [PATCH 1/2] audio: honor QEMU_AUDIO_TIMER_PERIOD instead of waking up every *nano* second

[Paolo Bonzini <pbonzini@redhat.com>]

Il 10/10/2013 11:23, Hans de Goede ha scritto:
> Hi,
> 
> On 9 Oct 2013, at 20:42, Hans de Goede wrote:
>>
>> Now that we no longer have MIN_REARM_TIMER_NS a bug in the audio
>> subsys has
>> clearly shown it self by trying to make a timer fire every nano second.
>>
>> Note we have a similar problem in 1.6, 1.5 and older but there
>> MIN_REARM_TIMER_NS limits the wakeups caused by audio being active to
>> 4000 times / second. This still causes a host cpu load of 50 % for simply
>> playing audio, where as with this patch git master is at 13%, so we
>> should
>> backport this to 1.5 and 1.6 too.
> 
> I'm still not sure when this actually started happening, but looking at
> RHEL-6 qemu sources to see if that has the issue too, I've learned how
> this problem was introduced, the audio_timer callback used to do this:
> 
>     qemu_mod_timer (s->ts, qemu_get_clock (vm_clock) + conf.period.ticks);
> 
> instead of calling audio_reset_timer(), so in the past there were 2
> mod_timer
> calls, one from audio_reset_timer(), which scheduled the callback to run
> ASAP, and one from the audio_timer callback honering conf.period.hertz.
> 
> Then at some point the qemu_mod_timer call in audio_timer was replaced
> with calling audio_reset_timer() and we got the problem my patch fixes.

The first broken version seems to be 0.14.0:

commit 39deb1e496de81957167daebf5cf5d1fbd5e47c2
Author: malc <av1474@comtv.ru>
Date:   Thu Nov 18 14:30:12 2010 +0300

    audio: Only use audio timer when necessary

    Originally proposed by Gerd Hoffmann.

    Signed-off-by: malc <av1474@comtv.ru>
    Acked-by: Gerd Hoffmann <kraxel@redhat.com>