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 11:27:37 +0100
Message-ID: <s5hsgkf7l2e.wl-tiwai@suse.de> (raw)
In-Reply-To: <97bbe88d1a6b63fe8e9b02bf0c5ce4a80553c48d.camel@linux.intel.com>

On Thu, 16 Jan 2020 10:50:33 +0100,
Keyon Jie wrote:
> 
> On Thu, 2020-01-16 at 08:15 +0100, Takashi Iwai wrote:
> > On Thu, 16 Jan 2020 05:53:18 +0100,
> > Keyon Jie wrote:
> > > With today's code, we preallocate DMA buffer for substreams at
> > > pcm_new()
> > > stage, and the substream->buffer_bytes_max and substream->dma_max
> > > will
> > > save as the actually preallocated buffer size and maximum size that
> > > the
> > > dma buffer can be expanded by at hw_params() state,
> > > correspondingly.
> > 
> > No, it's other way round: the former, buffer_bytes_max, is the max
> > size defined by the driver (i.e. passed in snd_pcm_hardware) and the
> > latter, dma_max, is the max preallocation size (passed to
> > preallocation helper).
> 
> Hi Takashi, thanks for your comment.
> 
> First of all, have you ever hit issue I mentioned in the commit message
> that we can't set buffer_bytes larger than the preallocated dma bytes?
> 
> I found this issue in kinds of platforms, not only on SOF/SoC ones, but
> also on legacy HDA ones.
> 
> Secondly, I am not clear about the design intention of the substream-
> >buffer_bytes_max and substream->dma_max, if it is as you commented
> above, can you help answer my questions below inline the code?
> 
> void snd_pcm_lib_preallocate_pages(struct snd_pcm_substream *substream,
> 				  int type, struct device *data,
> 				  size_t size, size_t max)
> 
> static void preallocate_pages(struct snd_pcm_substream *substream,
> 			      int type, struct device *data,
> 			      size_t size, size_t max, bool managed)
> {
> ...
> 	if (substream->dma_buffer.bytes > 0)
> 		substream->buffer_bytes_max = substream-
> >dma_buffer.bytes;//Keyon: this is the actual allocated buffer bytes,
> what is the intention here and why it is assigned to buffer_bytes_max
> which will be used to constrain on the _HW_PARAM_BUFFER_BYTES later?
> 
> 	substream->dma_max = max; //Keyon: looks here it is where the
> *max* param used only if we don't define SND_VERBOSE_PROCFS? what
> relationship can we have with the preallocation itself?
> ...
> }

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).

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.


thanks,

Takashi

---
diff --git a/sound/core/pcm_memory.c b/sound/core/pcm_memory.c
index d4702cc1d376..6a6c3469bbcd 100644
--- a/sound/core/pcm_memory.c
+++ b/sound/core/pcm_memory.c
@@ -96,6 +96,29 @@ void snd_pcm_lib_preallocate_free_for_all(struct snd_pcm *pcm)
 }
 EXPORT_SYMBOL(snd_pcm_lib_preallocate_free_for_all);
 
+/* set up substream->buffer_bytes_max, which is used in hw_constraint */
+static void set_buffer_bytes_max(struct snd_pcm_substream *substream,
+				 size_t size)
+{
+	substream->buffer_bytes_max = UINT_MAX;
+
+	if (!size)
+		return; /* no preallocation */
+
+	/* for SG-buffers, no limitation is needed */
+	switch (substream->dma_buffer.dev.type) {
+#ifdef CONFIG_SND_DMA_SGBUF
+	case SNDRV_DMA_TYPE_DEV_SG:
+	case SNDRV_DMA_TYPE_DEV_UC_SG:
+#endif
+	case SNDRV_DMA_TYPE_VMALLOC:
+		return;
+	}
+
+	/* for continuous buffers, limit to the preallocated size */
+	substream->buffer_bytes_max = size;
+}
+
 #ifdef CONFIG_SND_VERBOSE_PROCFS
 /*
  * read callback for prealloc proc file
@@ -156,10 +179,8 @@ static void snd_pcm_lib_preallocate_proc_write(struct snd_info_entry *entry,
 				buffer->error = -ENOMEM;
 				return;
 			}
-			substream->buffer_bytes_max = size;
-		} else {
-			substream->buffer_bytes_max = UINT_MAX;
 		}
+		set_buffer_bytes_max(substream, size);
 		if (substream->dma_buffer.area)
 			snd_dma_free_pages(&substream->dma_buffer);
 		substream->dma_buffer = new_dmab;
@@ -206,10 +227,8 @@ static void preallocate_pages(struct snd_pcm_substream *substream,
 
 	if (size > 0 && preallocate_dma && substream->number < maximum_substreams)
 		preallocate_pcm_pages(substream, size);
-
-	if (substream->dma_buffer.bytes > 0)
-		substream->buffer_bytes_max = substream->dma_buffer.bytes;
 	substream->dma_max = max;
+	set_buffer_bytes_max(substream, substream->dma_buffer.bytes);
 	if (max > 0)
 		preallocate_info_init(substream);
 	if (managed)
_______________________________________________
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 [this message]
2020-01-16 11:25       ` Keyon Jie
2020-01-16 11:50         ` Takashi Iwai
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=s5hsgkf7l2e.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