Messages in this thread | | | Date | Sun, 1 Nov 2020 19:52:38 -0800 | From | Andi Kleen <> | Subject | Re: [PATCH v2 0/4] perf: Fix perf_event_attr::exclusive rotation |
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> hm, it's too late for me to check ;-) but should I be able to do > this with exclusive event.. running both command at the same time:
Yes. The exclusive part only applies during a given context, but the two commands are different contexts.
You would only see a difference when in the same context, and you have multiple groups (or events) that could in theory schedule in parallel
e.g. something like
perf stat -e '{cycles,cycles},{cycles,cycles}' ...
The main motivation is actually that the "multiple groups" algorithm in perf doesn't work all that great: it has quite a few cases where it starves groups or makes the wrong decisions. That is because it is very difficult (likely NP complete) problem and the kernel takes a lot of short cuts to avoid spending too much time on it.
With exclusive it will be possible for a tool to generate "perfect groups" in user space and assume the kernel schedules it dumbly, but at least without any starvation.
-Andi
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