Re: Instrumenting context switches

[Dave Sperry <dave_sperry@ieee.nospam.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);
> > }
> >
> >
> >
> 
>