On Thu, 31 May 2018 09:43:10 +0200, Zengtao (B) wrote: > > 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. The timeout isn't about guaranteeing anything. It's merely a last-resort safeguard. So it *has to* be long, per definition. That is, if you hit this timeout, it means that something is already wrong. In that case, fix the real cause instead of tweaking the timeout. Takashi > 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
