[alsa-devel] [PATCH] ALSA: pcm: fix buffer_bytes max constrained by preallocated bytes issue

[Rajwa, Marcin]

On 1/16/2020 5:39 PM, Pierre-Louis Bossart wrote:
>
>>> So, do you suggest not doing preallocation(or calling it with 0 
>>> size) for all
>>> driver with TYPE_SG? I am fine if this is the recommended method, I 
>>> can try
>>> this on SOF I2S platform to see if it can work as we required for 
>>> very large
>>> buffer size.
>
> Keyon, for the rest of us to follow this patch, would you mind 
> clarifying what drives the need for a 'very large buffer size', and 
> what order of magnitude this very large size would be.
>
> FWIW, we've measured consistently on different Windows/Linux 
> platforms, maybe 10 years ago, that once you reach a buffer of 1s (384 
> kB) the benefits from increasing that buffer size further are marginal 
> in terms of power consumption, and generate all kinds of issues with 
> volume updates and deferred routing changes.
>
We need bigger buffer on host side to compensate the wake up time from 
d0ix to d0 which takes ~2 seconds on my setup. So, wiith smaller buffer 
sizes like < 2 seconds we overwrite data since FW keeps copping while 
host doesn't read until its up and running again.

> Thanks
> -Pierre
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