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Message-ID: <20201102035238.GI466880@tassilo.jf.intel.com> Date: Sun, 1 Nov 2020 19:52:38 -0800 From: Andi Kleen <ak@...ux.intel.com> To: Jiri Olsa <jolsa@...hat.com> Cc: Peter Zijlstra <peterz@...radead.org>, mingo@...nel.org, acme@...nel.org, mark.rutland@....com, alexander.shishkin@...ux.intel.com, namhyung@...nel.org, linux-kernel@...r.kernel.org, eranian@...gle.com Subject: Re: [PATCH v2 0/4] perf: Fix perf_event_attr::exclusive rotation > 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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