On 02.09.2015 19:00, Vince Weaver wrote:
They might not be relevant for profiling, but some people use the perf
counters for other tasks.
For example, when measuring phase plot behavior for a system, it would be
great if you'd be able to say I want a snapshot sample of the cycle and
instruction counters every 10ms, and then you can plot the CPI behavior of
the system.
Yeah, actually I wasn't asking about profiling, sorry if this was
misunderstood for some reason. I am looking into something you could
call 'workload characterization' and really need the absolute
performance counter values, as they could for example correlate with the
resulting temperature or energy-optimal frequency of the cpu/system,
depending on its specific workload.
as far as I can tell you can't really do this with perf (the -I option
only lets you get down to 100ms).
Which -I option do you mean? At least it's not available for my perf
record (kernel 3.16).
I ended up trying to write a custom program to do this, but it turns out
the perf sampling interface has really high overhead when doing this, and
the interrupt throttle kicks in which makes it useless.
Are you talking about the kernel interface or some interface of the perf
tool? I think I need a minimum of 100Hz or 1000Hz, but it wouldn't be a
problem if this is just collected in some kernel shared memory and in
the end copied to userspace, or at a lower frequency.
It's a shame, as the old "pfmon" tool that came with perfmon2 could do
this kind of measurement very easily.
Vince
This can not be used with current kernels, I guess? I tried "oprofile"
before, which can show absolute counts, but instead doesn't support any
timestamps.
So, it seems there is nothing available that can do what I need. Maybe
some of you can still recommend where I could start looking next or go
into more detail? Kernel, perf, oprofile, libpapi are the things that
come to my mind. If the kernel interface is really the bottleneck, it
probably has to be there.
Thanks for your help so far,
Dennis
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