On Wed, 6 Jan 2010, pl bossart wrote: >>> A wake-up is generated during the period interrupt, and a second >>> wake-up is generated during the write loop, after the application was >>> awaken but just before the pointers are updated. This second wake-up >>> shouldn't exist, since the write loop actually fills the ring buffer. >>> By the time the second wake-up is actually handled, there's really no >>> space left in the buffer and a null event is generated; it'll wake-up >>> the application a second time for nothing. Maybe we should move the >>> call to snd_pcm_update_hw_ptr() after the transfer took place? >> >> The right fix should be to preserve wakeups when write operation is in >> progress (also for interrupts). Something like this (untested): > > Thanks Jaroslav for your feedback. It seems your fix is similar to > what I suggested, that is check the pointers and generate a wake-up > after the write loop completes rather than right before the write > starts. I modified your patch to correct the behavior when errors > occur; the jumps to _end_wake compared to _end_unlock weren't self > explanatory and not always consistent. I only perform a pointer update > if nothing wrong happened. In case of errors, I unlock or just return > the status as before. I am testing the changes and should have a patch > shortly. > Cheers The improved and more clean fix in now in my tree: http://git.alsa-project.org/?p=alsa-kernel.git;a=commitdiff;h=1250932e48d3b698415b1f04775433cf1da688d6 Note that you should apply these 4 patches (in reverse order): 4: ALSA: pcm_lib - optimize wake_up() calls for PCM I/O 3: ALSA: pcm_lib - cleanup & merge hw_ptr update functions 2: ALSA: pcm_lib - add possibility to log last 10 DMA ring buffer positions 1: ALSA: pcm_lib.c - convert second xrun_debug() parameter to use defines Patch #3 should definitely fix problems with large avail or delay values reported in PA. I finally figured the culprit (and decide to cleanup all relevant code rather do just another workaround). In other words, new hw_ptr pointer should never be less than previous one now. Jaroslav ----- Jaroslav Kysela <perex@xxxxxxxx> Linux Kernel Sound Maintainer ALSA Project, Red Hat, Inc. _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
