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Re: Issues getting IO times using Schedtimes.stp example script
- From: David Smith <dsmith at redhat dot com>
- To: Josh Stone <jistone at redhat dot com>
- Cc: Sunny Fugate <fugate at unm dot edu>, systemtap at sourceware dot org
- Date: Tue, 31 Jan 2012 15:02:41 -0600
- Subject: Re: Issues getting IO times using Schedtimes.stp example script
- References: <43C46BFF-CB0E-4155-BF0C-6ED3FF698D9B@unm.edu> <4F272C3B.9070000@redhat.com>
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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