• Takashi Iwai's avatar
    ALSA: pcm: Replace PCM hwptr tracking with tracepoints · f5914908
    Takashi Iwai authored
    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
    Signed-off-by: default avatarTakashi Iwai <tiwai@suse.de>