From: Song Liu <songliubraving@fb.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@kernel.org>,
lkml <linux-kernel@vger.kernel.org>,
"acme@kernel.org" <acme@kernel.org>,
"alexander.shishkin@linux.intel.com"
<alexander.shishkin@linux.intel.com>,
"jolsa@redhat.com" <jolsa@redhat.com>,
"eranian@google.com" <eranian@google.com>,
"tglx@linutronix.de" <tglx@linutronix.de>,
"alexey.budankov@linux.intel.com"
<alexey.budankov@linux.intel.com>,
"mark.rutland@arm.com" <mark.rutland@arm.com>,
"megha.dey@intel.com" <megha.dey@intel.com>,
"frederic@kernel.org" <frederic@kernel.org>
Subject: Re: [RFC][PATCH] perf: Rewrite core context handling
Date: Tue, 16 Oct 2018 16:34:05 +0000 [thread overview]
Message-ID: <9865C981-0E8C-4419-AE8C-638DCD40D74E@fb.com> (raw)
In-Reply-To: <20181016095056.GE4030@hirez.programming.kicks-ass.net>
> On Oct 16, 2018, at 2:50 AM, Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Sat, Oct 13, 2018 at 08:31:37AM +0000, Song Liu wrote:
>
>> The only suggestion I have right now is on which struct owns which
>> data:
>>
>> 1. perf_cpu_context owns two perf_event_context: ctx and *task_ctx.
>> This is the same as right now.
>
>> 2. perf_event_context owns multiple perf_event_pmu_context:
>> One perf_event_pmu_context for software groups;
>> One perf_event_pmu_context for each hardware PMU.
>
> It does now already, right? Through the pmu_ctx_list we can, given an
> perf_event_context, find all associated perf_event_pmu_context's.
Yes, this is very similar to right now. It is related to #4, #5 below.
With current patch, perf_cpu_pmu_context is more like the "owner" of
the per CPU perf_event_pmu_context. I feel it is more natural that
perf_cpu_context is the owner of perf_event_pmu_context, while the
perf_cpu_pmu_context doesn't own anything.
Again, the difference to current patch is very small.
>
>> 3. perf_event_pmu_context owns RB tree of events. Since we don't
>> need rotation across multiple hardware PMUs, the rotation is
>> within same perf_event_pmu_context.
>
> By keeping the RB trees in perf_event_context, we get bigger trees,
> which is more efficient (log(n+m) < log(n) + log(m))
>
> Also, specifically, it means we only need a single merge sort /
> iteration to schedule in a full context, instead of (again) doing 'n' of
> them.
>
> Also, given a context and a pmu, it is cheaper for finding the relevant
> events; this is needed for big.little for instance. Something the
> proposed patch doesn't fully flesh out.
Would it be faster if we add a perf_event_pmu_context pointer to the
perf_event? I think a group on hw PMU-a should never know a group on
hw PMU-b. So some separation would make things simpler.
Thanks,
Song
next prev parent reply other threads:[~2018-10-16 16:35 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-10-10 10:45 [RFC][PATCH] perf: Rewrite core context handling Peter Zijlstra
2018-10-11 7:50 ` Song Liu
2018-10-11 9:29 ` Peter Zijlstra
2018-10-11 22:37 ` Song Liu
2018-10-12 9:50 ` Peter Zijlstra
2018-10-12 14:25 ` Peter Zijlstra
2018-10-13 8:31 ` Song Liu
2018-10-16 9:50 ` Peter Zijlstra
2018-10-16 16:34 ` Song Liu [this message]
2018-10-16 18:10 ` Peter Zijlstra
2018-10-16 18:24 ` Song Liu
2018-10-12 7:04 ` Alexey Budankov
2018-10-12 11:54 ` Peter Zijlstra
2018-10-15 7:26 ` Alexey Budankov
2018-10-15 8:34 ` Peter Zijlstra
2018-10-15 8:53 ` Peter Zijlstra
2018-10-15 17:29 ` Alexey Budankov
2018-10-15 18:31 ` Stephane Eranian
2018-10-16 6:39 ` Alexey Budankov
2018-10-16 9:32 ` Peter Zijlstra
2018-10-15 22:09 ` Song Liu
2018-10-16 18:28 ` Song Liu
2018-10-17 11:06 ` Peter Zijlstra
2018-10-17 16:43 ` Song Liu
2018-10-17 17:19 ` Peter Zijlstra
2018-10-17 18:33 ` Peter Zijlstra
2018-10-17 18:57 ` Song Liu
2018-10-16 16:26 ` Mark Rutland
2018-10-16 18:07 ` Peter Zijlstra
2018-10-17 8:57 ` Alexey Budankov
2018-10-17 15:01 ` Alexander Shishkin
2018-10-17 15:58 ` Alexey Budankov
2018-10-17 16:30 ` Peter Zijlstra
2018-10-18 7:05 ` Alexey Budankov
2018-10-22 13:26 ` Alexander Shishkin
2018-10-23 6:13 ` Song Liu
2018-10-23 6:55 ` Peter Zijlstra
2019-05-15 11:17 ` Alexander Shishkin
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