On Fri, 17 Jan 2020 11:43:24 +0100, Keyon Jie wrote: > > > > On 2020/1/17 下午4:00, Takashi Iwai wrote: > > On Fri, 17 Jan 2020 06:37:16 +0100, > > Keyon Jie wrote: > >> > >> 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... > > > > Well, that's the case you'd need a larger preallocation. > > I guess many distros already set it to a higher value for PulseAudio. > > The default 64kB is just from historical and compatibility reason, and > > we may extend it to 1MB or so now. > > In SOF driver, we don't use kernel config item like > CONFIG_SND_HDA_PREALLOC_SIZE for HDA, the code for it is: > > snd_pcm_lib_preallocate_pages(pcm->streams[stream].substream, > SNDRV_DMA_TYPE_DEV_SG, sdev->dev, > le32_to_cpu(caps->buffer_size_min), > le32_to_cpu(caps->buffer_size_max)); > > So the preallocated size is configured via topology file, that is > caps->buffer_size_min, no chance for PulseAudio to reconfigure it. > > So, it looks like we have to change it to this if we don't change the > ALSA core: > > snd_pcm_lib_preallocate_pages(pcm->streams[stream].substream, > SNDRV_DMA_TYPE_DEV_SG, sdev->dev, > - le32_to_cpu(caps->buffer_size_min), > + le32_to_cpu(caps->buffer_size_max), > le32_to_cpu(caps->buffer_size_max)); Yes, passing buffer_size_min for the preallocation sounds already bad. The default value should be sufficient for usual operations, not the cost-cutting minimum. Otherwise there is no merit of preallocation. Alternatively, we may pass 0 there, indicating no limitation, too. But, this would need a bit other adjustment, e.g. snd_pcm_hardware should have lower buffer_bytes_max. Takashi _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx https://mailman.alsa-project.org/mailman/listinfo/alsa-devel
