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Re: Instrumenting context switches
- From: Dave Sperry <dave_sperry at ieee dot nospam dot dot dot org>
- To: perryche at us dot ibm dot com
- Cc: systemtap at sourceware dot org
- Date: Thu, 30 Nov 2006 17:01:25 -0500
- Subject: Re: Instrumenting context switches
- References: <OFB78608CD.65116F14-ON85257236.0073959D-85257236.00738AAF@mck.us.ray.com>
- Reply-to: dave_sperry at ieee dot nospam dot dot dot org
Perry,
I had no problem running your systemtap scripts on my AMD-686 SMP box
running the same kernel as you list below.
I did a stap perry.stp -vvvv -g &>perryFoo.txt and it worked just fine.
You can see the log at:
http://toomanyprojects.org:2000/outbound/perry/perryFoo.txt
The version of systemtap I used is:
SystemTap translator/driver (version 0.5.11 built 2006-11-20)
(Using Red Hat elfutils 0.124 libraries.)
Copyright (C) 2005-2006 Red Hat, Inc. and others
This is free software; see the source for copying conditions.
Dave
> Perry Cheng
> <perryche@us.ibm.
> com> To
> Sent by: Martin Hunt <hunt@redhat.com>,
> systemtap-owner@s systemtap@sourceware.org
> ourceware.org cc
>
> Subject
> 11/30/2006 03:29 Re: Instrumenting context switches
> PM
>
> The following even simpler program also dies and rules out gettimeofday or
> accessing a global variable as possible causes. The crash happens on both
> an intel-686 and AMD-686 both running a modified version of 2.6.16. I
> don't know the details of the modifications but they are generally used to
> support real-time features and include the hrt and rt-prio patches. The
> src is at ftp://linuxpatch.ncsa.uiuc.edu/rt-linux/rhel4u2/R1-iFix1.
>
> If I replace __switch_to with context_switch or finish_task_switch, the
> failure still occurs. However, if I switch to set_task_comm, then things
> seem ok.
>
> probe kernel.function("__switch_to")
> {
> foobar()
> }
>
> function foobar()
> %{
> _stp_printf("foobar\n");
> %}
>
> Perry
>
>
> systemtap-owner@sourceware.org wrote on 11/30/2006 10:31:10 AM:
>
> > On Wed, 2006-11-29 at 18:25 -0500, Perry Cheng wrote:
> >
> > > probe kernel.function("__switch_to")
> > > {
> > > doSwitchTo(gettimeofday_us(), $prev_p, $next_p);
> > > }
> > >
> > > function doSwitchTo(timeus:long, prev:long, next:long)
> > > %{
> > > _stp_printf("SWITCHCOUNT = %ld\n", switchCount);
> > > <------------------------------ BAD LINE
> > > switchCount++;
> > > }%
> >
> > Obviously the code fragment above is not exactly what you are using to
> > reproduce the bug. (You can't use keywords as parameter names,
> > uninitialized switchCount, "}%", etc). I tried the following and did
> > not see any problems. Can you give more details (arch, OS, etc) on how
> > to reproduce?
> >
> > %{
> > long switchCount = 1000000;
> > %}
> >
> > function doSwitchTo (t:long, p:long, n:long) %{
> > _stp_printf("SWITCHCOUNT = %ld\n", switchCount);
> > switchCount++;
> > %}
> >
> > probe kernel.function("__switch_to")
> > {
> > doSwitchTo(gettimeofday_us(), $prev_p, $next_p);
> > }
> >
> >
> >
>
>