Re: Proposed systemtap access to perfmon hardware

["Bill Rugolsky Jr." <brugolsky@telemetry-investments.com>]

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