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Re: Proposed systemtap access to perfmon hardware
On Fri, Mar 17, 2006 at 11:20:46AM -0500, William Cohen wrote:
> To try to get a feel on how the performance monitoring hardware support
> would work in SystemTap I wrote some simple examples. Below are examples
> for computing IPC, average cycle count, and sampling within a function.
> The IPC and average cycle count function need a bit of rework to work
> for a SMP machines.
>
> Let me know if there are comments or questions on the examples.
A non-statistical application for systemtap perfctrs:
In light of a suggestion made by Alan Cox yesterday,
http://lkml.org/lkml/2006/3/16/118
I'm hacking up some additions to Ingo Molnar's latency tracing patch
that will track retired insns as well as clock cycles, so I can see
where the processor is stalled on I/O, SMM traps, etc., within a given
execution path.
For the particular case that triggered the aforementioned thread, I know
the precise offending instruction, but in the general case a search
for the culprit might be necessary, and doing this with systemtap would
be convenient.
Regards,
Bill Rugolsky