> -----Original Message----- > From: Jie, Yang > Sent: Thursday, January 16, 2020 10:14 PM > To: 'Takashi Iwai' <tiwai@xxxxxxx>; Keyon Jie <yang.jie@xxxxxxxxxxxxxxx> > Cc: alsa-devel@xxxxxxxxxxxxxxxx > Subject: RE: [PATCH] ALSA: pcm: fix buffer_bytes max > constrained by preallocated bytes issue > > > -----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. Tried and found setting 0 size for preallocation doesn't work for me, I have even tried to setting the size as big as the max(which the user space may require for buffer-bytes), it still doesn't work for me. Thanks, ~Keyon > > Thanks, > ~Keyon > _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx https://mailman.alsa-project.org/mailman/listinfo/alsa-devel
