Hi Takashi: Thank you for your reply. >-----Original Message----- >From: Takashi Iwai [mailto:tiwai@xxxxxxx] >Sent: Sunday, May 13, 2018 6:40 PM >To: Zengtao (B) <prime.zeng@xxxxxxxxxxxxx> >Cc: perex@xxxxxxxx; tiwai@xxxxxxxx; alsa-devel@xxxxxxxxxxxxxxxx; >linux-kernel@xxxxxxxxxxxxxxx >Subject: Re: Timeout issues in wait_for_avail function > >On Mon, 07 May 2018 12:49:34 +0200, >Zengtao (B) wrote: >> >> Hi perex and tiwai: >> >> I have met a timeout case when capture audio from snd-usb-audio >> device, when the host call the pcm_read and get into the wait_for_avail >function. >> The following happends >> 1. No available data for capture(maybe because of the late response >> audio data by the uac device) > >Hrm, in the case of capture, the data must be available. >If it's not the case, something is wrong. > >> 2. The current thread falls into sleep state and no one wakes up it. >> 3. The current thread will sleep 10s(schedule_timeout(1000)) and then >wakeup. >> >> I have two question about the wait_for_avail: >> 1. The timeout value too long, is it a reasonable value? >> 2. Is there any mechanism to wake up the thread if there is data from the >hw. > >The scenario above shouldn't happen, so no need for discussion. >Rather we should check why it's woken up even though no data is available. > It really happens on my platform, and anyway 10 seconds timeout seems not a reasonable value. And I don't there is any guarantee that there must be avail data when we reach wait_for_avail, in fact, inside the wait_for_avail, there is branch when no data is available. >You can check the tracepoints to see the action of PCM stream, and confirm >whether it's really no data, or it's just lost by some reason (or looks as if so). > I trace the data flow, we reach the wait_for_avail function before the usb snd data arrives, so we wait until 10 seconds timeout. > >Takashi Regards Zengtao _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
