Re: [patch] Real-Time Preemption, -RT-2.6.10-rc2-mm2-V0.7.32-2

[Ingo Molnar]

* Gene Heskett <gene.heskett@xxxxxxxxxxx> wrote:

> I'd like to report a slight improvement in the reports from tvtime
> while running 32-6 with full preemtion turned on, cfq scheduler:
> 
> ------
> Dec  7 13:29:39 coyote kernel: wow!  That was a 15 millisec bump
> Dec  7 13:29:39 coyote kernel: `IRQ 8'[838] is being piggy.
> need_resched=0, cpu=0
> Dec  7 13:29:39 coyote kernel: Read missed before next interrupt
> -----
> Each second of the log contains about 27 of these, so its pretty
> steady.  Picture looks pretty good though.
>
> Although, that particular snip was taken from the log while I was
> *not* on the same screen as tvtime.  Switching back it its screen
> returned the slip times to the 22 millisecond area. [...]

could enable WAKEUP_TIMING and LATENCY_TRACING, boot into the new kernel
and do:

	echo 0 > /proc/sys/kernel/preempt_max_latency

then you'll get the worst-case trace in /proc/latency_trace. Does it
show any millisecs-range latencies?

also, do this:

  chrt -f 90 -p `pidof 'IRQ 8'`
  chrt -f 91 -p `pidof 'IRQ 0'`

to make sure IRQ8 doesnt get preempted by other stuff. How often do you
get the rtc histogram in the syslog? Does tvtime use /dev/rtc for normal
operations perhaps? If yes then you might want to disable RTC_HISTOGRAM.

	Ingo
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