On Tue, 2 Nov 2010, Takashi Iwai wrote: > At Tue, 2 Nov 2010 09:26:48 +0100 (CET), > Jaroslav Kysela wrote: >> >> On Tue, 2 Nov 2010, Takashi Iwai wrote: >> >>> At Tue, 2 Nov 2010 09:17:33 +0100 (CET), >>> Jaroslav Kysela wrote: >>>> >>>> On Tue, 2 Nov 2010, Takashi Iwai wrote: >>>> >>>>> At Mon, 1 Nov 2010 17:12:53 -0500, >>>>> Pierre-Louis Bossart wrote: >>>>>> >>>>>> Merged and cleaned patch based on earlier patches posted >>>>>> on alsa-devel by Clemens Ladisch <clemens@xxxxxxxxxx> and >>>>>> Pierre-Louis Bossart <pierre-louis.bossart@xxxxxxxxx> >>>>>> >>>>>> This patch disables period interrupts which are not >>>>>> needed when the application relies on a system timer >>>>>> to wake-up and refill the ring buffer. The behavior of >>>>>> the driver is left unchanged, and interrupts are only >>>>>> disabled if the application requests this configuration. >>>>>> The behavior in case of underruns is slightly different, >>>>>> instead of being detected during the period interrupts the >>>>>> underruns are detected when the application calls >>>>>> snd_pcm_update_avail, which in turns forces a refresh of the >>>>>> hw pointer and shows the buffer is empty. >>>>> >>>>> So, this silently assumes that the applications do call >>>>> snd_pcm_update_avail() appropriately at the right timing? >>>>> If so, any sense to check XRUN in the driver at all...? >>>>> >>>>> And, even more, any sense to report the incremental position by this >>>>> approach? The only reliable information in this case is the offset in >>>>> the ring buffer. The linear position as the current ALSA API provides >>>>> isn't guaranteed without the period irq. >>>> >>>> We can detect the buffer size crossing using jiffies, but I agree, it's >>>> something which should be added to the patch to not break hw_ptr in >>>> case when the application does not call the update function in time. >>>> We have both values in runtime->hw_ptr_jiffies and >>>> runtime->hw_ptr_buffer_jiffies. >>> >>> But I thought this patch also disabled the jiffies check? >> >> These values are not related only to the debug jiffies check. I'm using >> these values also to detect the double irq acks which were discovered >> recently. > > Ah, OK, I overlooked it. > >>> I feel that some bottom-line check is needed if we keep the linear >>> position over the buffer size even without the period irq. >>> If the app doesn't care, OK fine, the driver shouldn't care, too. >>> But then it doesn't make sense to keep the linear position, either. >> >> But if we can keep the linear position using the light-weight jiffies >> check, it's probably OK to keep it rather than changing the hw_ptr >> behaviour. > > Well, but the point of the patch is to avoid wakeups as much as > possible. The jiffies-check adds an unconditional wakeup for each > buffer size, thus it's against the purpose of the patch. I don't see any wakeup. It's just about to compare the current jiffies with last hw_ptr update jiffies. The multiple buffer size crossing can be detected. > So, basically we need to decide whether > - to check via jiffies as a bottom-line; then no big merit over period=1 No, the difference is that no interrupts are really required. 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
