From: Andi Kleen <ak@linux.intel.com>
To: Jiri Olsa <jolsa@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
mingo@kernel.org, acme@kernel.org, mark.rutland@arm.com,
alexander.shishkin@linux.intel.com, namhyung@kernel.org,
linux-kernel@vger.kernel.org, eranian@google.com
Subject: Re: [PATCH v2 0/4] perf: Fix perf_event_attr::exclusive rotation
Date: Sun, 1 Nov 2020 19:52:38 -0800 [thread overview]
Message-ID: <20201102035238.GI466880@tassilo.jf.intel.com> (raw)
In-Reply-To: <20201031234418.GE3380099@krava>
> 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
next prev parent reply other threads:[~2020-11-02 3:52 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-29 16:27 [PATCH v2 0/4] perf: Fix perf_event_attr::exclusive rotation Peter Zijlstra
2020-10-29 16:27 ` [PATCH v2 1/4] perf: Simplify group_sched_out() Peter Zijlstra
2020-11-10 12:45 ` [tip: perf/urgent] " tip-bot2 for Peter Zijlstra
2020-10-29 16:27 ` [PATCH v2 2/4] perf: Simplify group_sched_in() Peter Zijlstra
2020-11-10 12:45 ` [tip: perf/urgent] " tip-bot2 for Peter Zijlstra
2020-10-29 16:27 ` [PATCH v2 3/4] perf: Fix event multiplexing for exclusive groups Peter Zijlstra
2020-11-10 12:45 ` [tip: perf/urgent] " tip-bot2 for Peter Zijlstra
2020-10-29 16:27 ` [PATCH v2 4/4] perf: Tweak perf_event_attr::exclusive semantics Peter Zijlstra
2020-11-10 12:45 ` [tip: perf/urgent] " tip-bot2 for Peter Zijlstra
2020-10-31 23:44 ` [PATCH v2 0/4] perf: Fix perf_event_attr::exclusive rotation Jiri Olsa
2020-11-02 3:52 ` Andi Kleen [this message]
2020-11-02 14:16 ` Peter Zijlstra
2020-11-03 2:41 ` Andi Kleen
2020-11-09 11:48 ` Peter Zijlstra
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