Issues getting IO times using Schedtimes.stp example script

[David Smith]

On 01/30/2012 05:48 PM, Josh Stone wrote:

> On 01/30/2012 03:13 PM, Sunny Fugate wrote:
>> I'm having some difficulties in getting one of the examples scripts to 
>> run.  According to the documentation, the kernel.trace("sched_switch") 
>> probe should expose $prev, $next, and $rq.  I've played around with the 
>> stp script and on my system the $rq variable is never defined.
> 
> There used to be a rq parameter, but it was removed from the kernels
> 2.6.35+ by commit 27a9da65:
> 
> http://git.kernel.org/?p=linux/kernel/git/torvalds/linux.git;a=commitdiff;h=27a9da6538ee18046d7bff8e36a9f783542c54c3
> 
> I don't know any other way off-hand to get at the runqueue -- it is held
> very secretively in sched internals.


I wonder if we couldn't set a kprobe on finish_task_switch() (which gets
an rq parameter).  We'd have to match the calls up, but it might be
possible.

-- 
David Smith
dsmith@redhat.com
Red Hat
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