[pulseaudio-discuss] [PATCH] Do not use tsched watermark if tsched is disabled

Colin Guthrie gmane at colin.guthr.ie
Wed Sep 1 00:39:39 PDT 2010

'Twas brillig, and David Henningsson at 01/09/10 08:36 did gyre and gimble:
> On 2010-08-31 17:57, Colin Guthrie wrote:
>> 'Twas brillig, and pl bossart at 19/08/10 14:52 did gyre and gimble:
>>>>> Assuming your reasoning is correct (I'm not that deep into DMA yet),
>>>>> this should be fixed in the kernel - by not allowing rewinds further
>>>>> back than 128 (or 256) bytes ahead of actual position.
>>>>> You say HDA can transfer up to 128 bytes in advance, but what about
>>>>> all
>>>>> the other drivers? Could there be other drivers having a lot larger
>>>>> DMA
>>>>> fetches?
>>>> What's the role of snd_pcm_rewindable()[1]? The documentation says "Get
>>>> safe count of frames which can be rewinded", which sounds to me like
>>>> the
>>>> function should always be called before snd_pcm_rewind(). Currently PA
>>>> doesn't call _rewindable().
>>> Yes it should be fixed in the kernel, but the DMA transfer size is not
>>> necessarily documented and known. Worse, it can vary depending on the
>>> mode. So until the kernel folks figure out a solution, and said
>>> solution works for all know drivers, this patch is mandatory on the
>>> PulseAudio side.
>> Don't want to lose momentum on this patch, so just poking about.
> Good initiative.
>> What is the next stage here?
> Probably either one will work, but if we're about to release 0.9.22
> (heard something from Lennart yet?), I suggest we go with my version for
> 0.9.22 as that one is the least invasive (only touches non-tsched
> devices), and keep Pierre's version in master.

Sounds reasonable. Pierre, what's your take?

Spoke briefly to to Lennart, I think he was generally up for some kind
of release, but we'll wait for a couple weeks when F15 beta freeze hits
and thus his systemd work will be paused for a while at least and he can
focus some of his time back on PA :)



Colin Guthrie

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