Re: [git pull] scheduler changes for v2.6.26

From: Ingo Molnar
Date: Wed Apr 23 2008 - 05:47:17 EST



* Frans Pop <elendil@xxxxxxxxx> wrote:

> If I enable tracing with these settings, I get data in both trace
> *and* in latency_trace. Is the last correct? From
> http://lkml.org/lkml/2008/2/10/43 I got the impression that file
> should only be used if the "wakeup" tracer is active.

yeah, that's the intended behavior. 'trace' and 'latency_trace' are two
kinds of 'views' on the same set of tracer data (with a different output
format). They are both non-destructive - i.e. they dont deplete the
trace buffers.

there's even a third view: 'trace_pipe' - which depletes the trace
buffers and can be used to pipe trace data into a larger file:

cat trace_pipe > /tmp/large-trace.txt

i guess it would be less confusing if 'trace' and 'latency_trace' was
just a single 'view' and its behavior depended on iter_ctl settings. (In
fact, we could probably just get rid of latency_trace - it is a leftover
from -rt.)

> From the last run I've got three traces with 50000 entries (about a
> minute worth each). Traces 1 and 2 should each have two skips and
> trace 3 should have four. I've saved both the trace and latency_trace
> (ltrace) files.
>
> They are available at:
> http://people.debian.org/~fjp/tmp/kernel/sched/.

thanks, we'll have a look.

> BTW, did either of you actually look at the traces I sent for .24? I
> never got any feedback on those.

hm, i looked at them - i thought i mailed you about that but indeed i
didnt (sorry about that) - the traces were too short in scope - they
just covered a few dozen milliseconds in scope, while your description
said that the problem occured seconds into the trace.

> P.S. I've got group scheduling active in this config as my tests with
> .24 showed that did not make any difference. Can rerun without if
> needed.

no need to rerun - but if you do the next test it might make sense to
disable it, just to reduce the number of variables.

another thing - Peter observed skipping on NOHZ. Does your skipping go
away if you boot with 'nohz' and/or with CONFIG_NOHZ=y disabled in the
.config?

Ingo
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