From: "Jie, Yang" <yang.jie@intel.com>
To: Takashi Iwai <tiwai@suse.de>, Keyon Jie <yang.jie@linux.intel.com>
Cc: "alsa-devel@alsa-project.org" <alsa-devel@alsa-project.org>
Subject: Re: [alsa-devel] [PATCH] ALSA: pcm: fix buffer_bytes max constrained by preallocated bytes issue
Date: Thu, 16 Jan 2020 14:14:28 +0000 [thread overview]
Message-ID: <E7B1D079BA13FB44A978CC8F69C7D6A96F98EDB4@SHSMSX105.ccr.corp.intel.com> (raw)
In-Reply-To: <s5hh80v7h82.wl-tiwai@suse.de>
> -----Original Message-----
> From: Alsa-devel <alsa-devel-bounces@alsa-project.org> On Behalf Of
> Takashi Iwai
> Sent: Thursday, January 16, 2020 7:51 PM
> To: Keyon Jie <yang.jie@linux.intel.com>
> Cc: alsa-devel@alsa-project.org
> Subject: Re: [alsa-devel] [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@alsa-project.org
> https://mailman.alsa-project.org/mailman/listinfo/alsa-devel
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next prev parent reply other threads:[~2020-01-16 14:15 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-16 4:53 [alsa-devel] [PATCH] ALSA: pcm: fix buffer_bytes max constrained by preallocated bytes issue Keyon Jie
2020-01-16 7:15 ` Takashi Iwai
2020-01-16 9:50 ` Keyon Jie
2020-01-16 10:27 ` Takashi Iwai
2020-01-16 11:25 ` Keyon Jie
2020-01-16 11:50 ` Takashi Iwai
2020-01-16 14:14 ` Jie, Yang [this message]
2020-01-16 15:31 ` Jie, Yang
2020-01-16 16:07 ` Takashi Iwai
2020-01-16 16:39 ` Pierre-Louis Bossart
2020-01-16 17:25 ` Rajwa, Marcin
2020-01-16 17:40 ` Pierre-Louis Bossart
2020-01-16 20:37 ` Takashi Iwai
2020-01-17 5:30 ` Keyon Jie
2020-01-17 7:57 ` Takashi Iwai
2020-01-17 10:13 ` Keyon Jie
2020-01-17 10:30 ` Takashi Iwai
2020-01-17 10:56 ` Keyon Jie
2020-01-17 11:15 ` Takashi Iwai
2020-01-17 5:37 ` Keyon Jie
2020-01-17 8:00 ` Takashi Iwai
2020-01-17 10:43 ` Keyon Jie
2020-01-17 11:12 ` Takashi Iwai
2020-01-19 3:52 ` Keyon Jie
2020-01-19 7:09 ` Takashi Iwai
2020-01-19 8:11 ` Keyon Jie
2020-01-19 9:04 ` Takashi Iwai
2020-01-19 10:14 ` Keyon Jie
2020-01-19 10:43 ` Takashi Iwai
2020-01-20 2:23 ` Keyon Jie
2020-01-16 15:45 ` Takashi Iwai
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