Re: Instrumenting context switches

[Perry Cheng <perryche at us dot ibm dot com>]

Hi Dave,

I was using version 0.4 and have upgraded to version 0.5.11 like you 
(mine's from today though and not 11/20). 
However, the new stap can't find the probe points.  I suspect that it is 
not locating the kernel symbols file. 
Do you know how to get the info out of the old /usr/bin/stap and give it 
to the new /usr/local/bin/stap? 


Perry


systemtap-owner@sourceware.org wrote on 11/30/2006 05:01:25 PM:

> 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);
> > > }
> > >
> > >
> > >
> > 
> > 
>