Alsa-Devel Archive on lore.kernel.org
 help / color / Atom feed
From: Takashi Iwai <tiwai@suse.de>
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
Date: Thu, 16 Jan 2020 12:50:37 +0100
Message-ID: <s5hh80v7h82.wl-tiwai@suse.de> (raw)
In-Reply-To: <3c0a0067043d614cd4491b28acf6d49640746b15.camel@linux.intel.com>

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.

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.


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

  reply index

Thread overview: 31+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-01-16  4:53 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 [this message]
2020-01-16 14:14           ` Jie, Yang
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

Reply instructions:

You may reply publically to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=s5hh80v7h82.wl-tiwai@suse.de \
    --to=tiwai@suse.de \
    --cc=alsa-devel@alsa-project.org \
    --cc=yang.jie@linux.intel.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link

Alsa-Devel Archive on lore.kernel.org

Archives are clonable:
	git clone --mirror https://lore.kernel.org/alsa-devel/0 alsa-devel/git/0.git

	# If you have public-inbox 1.1+ installed, you may
	# initialize and index your mirror using the following commands:
	public-inbox-init -V2 alsa-devel alsa-devel/ https://lore.kernel.org/alsa-devel \
		alsa-devel@alsa-project.org
	public-inbox-index alsa-devel

Example config snippet for mirrors

Newsgroup available over NNTP:
	nntp://nntp.lore.kernel.org/org.alsa-project.alsa-devel


AGPL code for this site: git clone https://public-inbox.org/public-inbox.git