Re: Latency data - 2.6.14-rc3-rt13

From: Mark Knecht
Date: Mon Oct 10 2005 - 18:50:06 EST

On 10/10/05, Mark Knecht <markknecht@xxxxxxxxx> wrote:
> On 10/10/05, Daniel Walker <dwalker@xxxxxxxxxx> wrote:
> > > Yes, already that looks interesting. Do I have something going on with
> > > acpi? This is before running Jack. I'm in Gnome.There are a lot of
> > > these messages, but they've stopped. I suppose the 3997 is the delay?
> > > That would coorespond with the info I sent earlier.
> >
> > I think this is a false reading . Sometimes when a system goes idle it
> > will cause interrupt disable latency that isn't real (due to process
> > halting) . You could try turning ACPI off if you can , and turn off
> > power management ..
> >
> > Daniel
> OK. NO immediate difference with most of the power management stuff
> turned off. I'll just let it run a few hours and see if I get an xrun.
> If I do I'll look at the logs again and report back.
> Thanks for the help. I feel like I've got a chance of spotting something.
> Cheers,
> Mark

Well, I'm disappointed again. Some xruns came but no additional data
was put into the dmesage file:

( softirq-timer/0-3 |#0): new 3997 us maximum-latency critical section.
=> started at timestamp 253995015: <acpi_processor_idle+0x20/0x379>
=> ended at timestamp 253999013: <thread_return+0xb5/0x11a>

Call Trace:<ffffffff8014e32c>{check_critical_timing+492}
<ffffffff803ec945>{schedule+261} <ffffffff801371ca>{ksoftirqd+138}
<ffffffff80137140>{ksoftirqd+0} <ffffffff8014740d>{kthread+205}
<ffffffff8010e6e6>{child_rip+8} <ffffffff80147340>{kthread+0}
| preempt count: 00000001 ]
| 1-level deep critical section nesting:
.. [<ffffffff803ec238>] .... __schedule+0xb8/0x5a6
.....[<00000000>] .. ( <= 0x0)

=> dump-end timestamp 253999092

kjournald starting. Commit interval 5 seconds
EXT3 FS on sdb1, internal journal
EXT3-fs: mounted filesystem with ordered data mode.
lightning ~ #

Basically the trace above was there pretty much right after booting. I
mounted a 1394 drive, which is shown, and then started running apps. I
got 3 xruns:

16:42:59.826 XRUN callback (1).
**** alsa_pcm: xrun of at least 0.273 msecs
16:43:03.764 XRUN callback (2).
**** alsa_pcm: xrun of at least 2.082 msecs
16:43:41.618 XRUN callback (3).
**** alsa_pcm: xrun of at least 2.040 msecs

but no additional data in the logs.

So possibly this is an IRQ off latency? Or am I jumping to
conclusions? The trace above, if I understand it, indicates a delay of
nearly 4mS, and again, since I'm trying to run at sub 3mS, that would
seem like a potential problem.

I'm going to completely shut off power management as a test just to
see where that leads.

- Mark
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