Re: [Xen-devel] [PATCH v5] sndif: add ABI for Para-virtual sound

[Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>]

Oleksandr Dmytryshyn writes ("Re: [Xen-devel] [PATCH v5] sndif: add ABI for 
Para-virtual sound"):
> On Thu, Jan 22, 2015 at 5:56 PM, Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx> 
> wrote:
> > Oleksandr Dmytryshyn writes ("Re: [Xen-devel] [PATCH v5] sndif: add ABI for 
> > Para-virtual sound"):
> >> In my case this is about 3 packets per second with size about 16 KBytes.
> >
> > That would put a floor on the latency of about 300ms.  I suspect
> > that's quite undesirable.
>
> This latency doesn't affect us because frontend and backend driver have
> an separate thread for each virtualized stream. And when frontend driver
> waits answer from the backend it just sleeps (in case Linux kernel it waits
> for the completion).

Your seem to be answering a different question to the one I intended
to ask.

What I mean is this:

Many people think it is important to reduce the latency of sound input
and output.  So, they want to reduce (a) the time between a piece of
software deciding to make a sound and (b) the time when that sound
starts to appear.  And the same for input.  This is important for
games, video conversations, and so on.

When sound output is occurring continuously, any piece of new sound
output needs to wait for the next packet to be sent.

If you are sending only 3 packets per second then the latency might be
as much as 1/3 second which I think is probably too much.

Ian.

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