On 2020/1/17 上午1:40, 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.
Right, that's a valid case, but that's 256 kB, not 'very large' or
likely to ever trigger an OOM case.
For S24_LE, it is 512KB, the point is that if we can't re-allocate
buffer at hw_params() stage, then we need follow a BKM that we have to
preallocate the largest DMA buffer that we claim to support at
pcm_new(), I think this is actually another kind of wast with these
largest pinned buffer that can't be swapped out...
Thanks,
~Keyon
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