ALSA: pcm: Replace PCM hwptr tracking with tracepoints

ALSA PCM core has a mechanism tracking the PCM hwptr updates for
analyzing XRUNs.  But its log is limited (up to 10) and its log output
is a kernel message, which is hard to handle.

In this patch, the hwptr logging is moved to the tracing
infrastructure instead of its own.  Not only the hwptr updates but
also XRUN and hwptr errors are recorded on the trace log, so that user
can see such events at the exact timing.

The new "snd_pcm" entry will appear in the tracing events:
  # ls -F /sys/kernel/debug/tracing/events/snd_pcm
  enable  filter  hw_ptr_error/  hwptr/  xrun/

The hwptr is for the regular hwptr update events.  An event trace
looks like:

  aplay-26187 [004] d..3  4012.834761: hwptr: pcmC0D0p/sub0: POS: pos=488, old=0, base=0, period=1024, buf=16384

"POS" shows the hwptr update by the explicit position update call and
"IRQ" means the hwptr update by the interrupt,
i.e. snd_pcm_period_elapsed() call.  The "pos" is the passed
ring-buffer offset by the caller, "old" is the previous hwptr, "base"
is the hwptr base position, "period" and "buf" are period- and
buffer-size of the target PCM substream.
(Note that the hwptr position displayed here isn't the ring-buffer
 offset.  It increments up to the PCM position boundary.)

The XRUN event appears similarly, but without "pos" field.
The hwptr error events appear with the PCM identifier and its reason
string, such as "Lost interrupt?".

The XRUN and hwptr error reports on kernel message are still left, can
be turned on/off via xrun_debug proc like before.  But the bit 3, 4, 5
and 6 bits of xrun_debug proc are dropped by this patch.  Also, along
with the change, the message strings have been reformatted to be a bit
more consistent.

Last but not least, the hwptr reporting is enabled only when
CONFIG_SND_PCM_XRUN_DEBUG is set.

Signed-off-by: Takashi Iwai <tiwai@suse.de>

1 files changed, 0 insertions, 13 deletions

diff --git a/Documentation/sound/alsa/Procfile.txt b/Documentation/sound/alsa/Procfile.txt
index 7fcd1ad..cfc4956 100644
--- a/Documentation/sound/alsa/Procfile.txt
+++ b/Documentation/sound/alsa/Procfile.txt
@@ -101,10 +101,6 @@ card*/pcm*/xrun_debug
 	  bit 0 = Enable XRUN/jiffies debug messages
 	  bit 1 = Show stack trace at XRUN / jiffies check
 	  bit 2 = Enable additional jiffies check
-	  bit 3 = Log hwptr update at each period interrupt
-	  bit 4 = Log hwptr update at each snd_pcm_update_hw_ptr()
-	  bit 5 = Show last 10 positions on error
-	  bit 6 = Do above only once
 
 	When the bit 0 is set, the driver will show the messages to
 	kernel log when an xrun is detected.  The debug message is
@@ -121,15 +117,6 @@ card*/pcm*/xrun_debug
 	buggy) hardware that doesn't give smooth pointer updates.
 	This feature is enabled via the bit 2.
 
-	Bits 3 and 4 are for logging the hwptr records.  Note that
-	these will give flood of kernel messages.
-
-	When bit 5 is set, the driver logs the last 10 xrun errors and
-	the proc file shows each jiffies, position, period_size,
-	buffer_size, old_hw_ptr, and hw_ptr_base values.
-
-	When bit 6 is set, the full xrun log is shown only once.
-
 card*/pcm*/sub*/info
 	The general information of this PCM sub-stream.