> -----Original Message----- > From: Alsa-devel <alsa-devel-bounces@xxxxxxxxxxxxxxxx> On Behalf Of > Takashi Iwai > Sent: Thursday, January 16, 2020 7:51 PM > To: Keyon Jie <yang.jie@xxxxxxxxxxxxxxx> > Cc: alsa-devel@xxxxxxxxxxxxxxxx > Subject: Re: [PATCH] ALSA: pcm: fix buffer_bytes max > constrained by preallocated bytes issue > > On Thu, 16 Jan 2020 12:25:38 +0100, > Keyon Jie wrote: > > > > On Thu, 2020-01-16 at 11:27 +0100, Takashi Iwai wrote: > > > On Thu, 16 Jan 2020 10:50:33 +0100, > > > > > > Oh, you're right, and I completely misread the patch. > > > > > > Now I took a coffee and can tell you the story behind the scene. > > > > > > I believe the current code is intentionally limiting the size to the > > > preallocated size. This limitation was brought for not trying to > > > allocate a larger buffer when the buffer has been preallocated. In > > > the past, most hardware allocated the continuous pages for a buffer > > > and the allocation of a large buffer fails quite likely. This was > > > the reason of the buffer preallocation. So, the driver wanted to > > > tell the user-space the limit. If user needs to have an extra large > > > buffer, they are supposed to fiddle with prealloc procfs (either > > > setting zero to clear the preallocation or setting a large enough > > > buffer beforehand). > > > > Thank you for the sharing, it is interesting and knowledge learned to > > me. > > > > > > > > For SG-buffers, though, limitation makes less sense than continuous > > > pages. e.g. a patch below removes the limitation for SG-buffers. > > > But changing this would definitely cause the behavior difference, > > > and I don't know whether it's a reasonable move -- I'm afraid that > > > apps would start hogging too much memory if the limitation is gone. > > > > I just went through all invoking to snd_pcm_lib_preallocate_pages*(), > > for those SNDRV_DMA_TYPE_DEV, some of them set the *size* equal to > the > > *max*, some set the *max* several times to the *size*, IMHO, the > > *max*s are matched to those hardware's limiatation, comparing to the > > *size*s, aren't they? > > > > In this case, I still think my patch hanle all > > TYPE_DEV/SNDRV_DMA_TYPE_DEV/TYPE_SG/SNDRV_DMA_TYPE_DEV > cases more > > gracefully, we will still take the limitation from the specific driver > > set, from the *max* param, and the test results looks very nice here, > > we will take what the user space wanted for buffer-bytes via aply > > exactly, as long as it is suitable for the interval and constraints. > > Well, I have a mixed feeling. Certainly we'd need some better way to allow a > larger buffer allocation, especially for HDA. OTOH, if the buffer was > preallocated, it's meant to be used actually. That's the point of the > hw_constraint setup. So if the buffer was preallocated, it won't be re-allocated at hw_params() stage, is this conflict with the re-allocate logic in hw_params()? > > And now thinking again after another cup of coffee, I wonder why we do > preallocate for HDA at all. For HD-audio, the allocation of any large buffer > would succeed very likely because of SG-buffer. > > So, just setting 0 to the preallocation size (but keeping else) would work, e.g. > something like below? The help text needs adjustment, but you can see the > rough idea. 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. Thanks, ~Keyon > > > thanks, > > Takashi > > --- a/sound/hda/Kconfig > +++ b/sound/hda/Kconfig > @@ -21,9 +21,10 @@ config SND_HDA_EXT_CORE > select SND_HDA_CORE > > config SND_HDA_PREALLOC_SIZE > - int "Pre-allocated buffer size for HD-audio driver" > + int "Pre-allocated buffer size for HD-audio driver" > if !SND_DMA_SGBUF > range 0 32768 > - default 64 > + default 64 if !SND_DMA_SGBUF > + default 0 if SND_DMA_SGBUF > help > Specifies the default pre-allocated buffer-size in kB for the > HD-audio driver. A larger buffer (e.g. 2048) is preferred > _______________________________________________ > Alsa-devel mailing list > Alsa-devel@xxxxxxxxxxxxxxxx > https://mailman.alsa-project.org/mailman/listinfo/alsa-devel _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx https://mailman.alsa-project.org/mailman/listinfo/alsa-devel
