On 12/17/18 5:54 PM, Takashi Iwai wrote: > On Fri, 14 Dec 2018 18:36:11 +0100, > Arnaud Rebillout wrote: >> Dear ALSA maintainers, >> >> I noticed big change in how long `snd_pcm_open()` takes, between kernel 4.16 >> and 4.17. With a kernel 4.16, this function consistently returns in less >> than 1 >> millisecond, with occasional, but rare, peaks that go up to 25ms. While with >> kernel 4.17 and above, I measure an average of 40ms, with frequent peaks >> to 1s. >> The maximum I measured was 3 seconds! >> >> Is this change known, intended? Or is it a regression? > If this happens at opening the PCM stream, it's likely a stall in > runtime PM resume by some reason. But I have no idea what actually > broke. > > Are you sure that it's a kernel regression, i.e. this doesn't happen > at all when booting the old kernel on the same system? > > If yes, the best would be to perform bisection. At least it'd be > helpful to narrow the regression a bit. > > And, this might be a known issue; I remember some report about the > long runtime PM resume on Dell XPS, which I can't see on other > machines. So it might be device-specific. I found out that this is actually due to a change in the debian kernel configuration. Starting from version 4.17, the kernel is configured with CONFIG_SND_HDA_POWER_SAVE_DEFAULT=1 (was =0 before). I could confirm that this is what makes snd_pcm_open() take much more time. I opened a bug at https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=917906. Thanks for the support! Arnaud _______________________________________________ Alsa-devel mailing list Alsa-devel@xxxxxxxxxxxxxxxx http://mailman.alsa-project.org/mailman/listinfo/alsa-devel
