Re: [PATCH] perf events: Add stalled cycles generic event - PERF_COUNT_HW_STALLED_CYCLES

[Arun Sharma <arun@sharma-home.net>]

On Wed, Apr 27, 2011 at 4:11 AM, Ingo Molnar <mingo@elte.hu> wrote:
> As for the first, 'overview' step, i'd like to use one or two numbers only, to
> give people a general ballpark figure about how good the CPU is performing for
> a given workload.
>
> Wouldnt UOPS_EXECUTED.CORE_ACTIVE_CYCLES,c=1,i=1 be in general a pretty good,
> primary "stall" indicator? This is similar to the "cycles-uops_executed" value
> in your script (UOPS_EXECUTED:PORT015:t=1 and UOPS_EXECUTED:PORT234_CORE
> based): it counts cycles when there's no execution at all - not even
> speculative one.

If we're going to pick one stall indicator, why not pick cycles where
no uops are retiring?

cycles_no_uops_retired = cycles - c["UOPS_RETIRED:ANY:c=1:t=1"]

In the presence of C-states and some halted cycles, I found that I
couldn't measure it via UOPS_RETIRED:ANY:c=1:i=1 because it counts
halted cycles too and could be greater than (unhalted) cycles.

The other issue I had to deal with was UOPS_RETIRED > UOPS_EXECUTED
condition. I believe this is caused by what AMD calls sideband stack
optimizer and Intel calls dedicated stack manager (i.e. UOPS executed
outside the main pipeline). A recursive fibonacci(30) is a good test
case for reproducing this.

>
> Is this the direction you'd like to see perf stat to move into? Any comments,
> suggestions?
>

Looks like a step in the right direction. Thanks.

 -Arun