On Fri, 17 Jan 2020 06:30:18 +0100, Keyon Jie wrote: > > On 2020/1/17 上午4:37, Takashi Iwai wrote: > > On Thu, 16 Jan 2020 18:40:26 +0100, > > 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. > > > > That size shouldn't matter, and would work even with the > > preallocation. > > > > My concern is that removing the limitation would allow the allocation > > of too large sizes. Even with dma_max limit, it can go up to 32MB > > physical pages per stream for HDA. Depending on the hardware setup, > > there can be a lot of streams assignment (e.g. HDMI codecs) and > > multiple codecs / controllers, and imagine that all those allocated > > pages are pinned and can't be swapped out... > > Hi Takashi, I get your concern here, but if we switch to use dma_max > limit, we won't change the preallocated buffer, it will be still 64KB > for each stream, user space can ask for re-allocate buffer for each > stream up to 32MB, but those pinned and can't be swapped out ones are > the 64KB preallocated ones only, am I wrong? No, in general, all sound hardware buffers are pinned. Takashi _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx https://mailman.alsa-project.org/mailman/listinfo/alsa-devel
