[alsa-devel] A bug about cache inconsistency report

[Takashi Iwai]

On Tue, 31 Jul 2018 12:52:04 +0200,
Hans Hu(SH-RD) wrote:
> 
> Hi All,
> 
>                Try send an email.
> 
>                Appearance:
> when use non-snoop + ioctl path combination, an issue occurs:
> usage: aplay -D plughw:0,0 44100_S16_LE_2c.wav
> Ubuntu, it performance intermittently noise;
> 
> Root case:
>                Function set_pages_array_wc marked the PTE of the original address; Function set_memory_wc marked the PTE both original and after vmaped address.
> [cid:image002.png at 01D428FF.92621520]
> However, cache or not in transmission process is based on the PTE of the later, and the set_pages_array_wc did't mark it, so a cache inconsistency issue occurs.
> 
>                Related bug:
>                SHA1 ID: 9ddf1aeb2134e72275c97a2c6ff2e3eb04f2f27a

OK, so did you confirm that dropping the SG buffer support "fixes" the
noise problem on your system?  The easiest test would be like:

--- a/sound/pci/hda/hda_controller.c
+++ b/sound/pci/hda/hda_controller.c
@@ -770,7 +770,7 @@ int snd_hda_attach_pcm_stream(struct hda_bus *_bus, struct hda_codec *codec,
 	size = CONFIG_SND_HDA_PREALLOC_SIZE * 1024;
 	if (size > MAX_PREALLOC_SIZE)
 		size = MAX_PREALLOC_SIZE;
-	snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV_SG,
+	snd_pcm_lib_preallocate_pages_for_all(pcm, SNDRV_DMA_TYPE_DEV,
 					      chip->card->dev,
 					      size, MAX_PREALLOC_SIZE);
 	return 0;


thanks,

Takashi