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

[Pierre-Louis Bossart]

>>>> 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.

Right, that's a valid case, but that's 256 kB, not 'very large' or 
likely to ever trigger an OOM case.