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Date:   Wed, 17 Oct 2018 18:30:21 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Alexey Budankov <alexey.budankov@linux.intel.com>
Cc:     mingo@kernel.org, linux-kernel@vger.kernel.org, acme@kernel.org,
        alexander.shishkin@linux.intel.com, jolsa@redhat.com,
        songliubraving@fb.com, eranian@google.com, tglx@linutronix.de,
        mark.rutland@arm.com, megha.dey@intel.com, frederic@kernel.org
Subject: Re: [RFC][PATCH] perf: Rewrite core context handling
Message-ID: <20181017163021.GP3121@hirez.programming.kicks-ass.net>
References: <20181010104559.GO5728@hirez.programming.kicks-ass.net>
 <f12f2d18-2e25-1879-fe34-227c82618abd@linux.intel.com>
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On Wed, Oct 17, 2018 at 11:57:49AM +0300, Alexey Budankov wrote:
> Hi,
> 
> On 10.10.2018 13:45, Peter Zijlstra wrote:
> <SNIP>
> > -static bool perf_rotate_context(struct perf_cpu_context *cpuctx)
> > +/*
> > + * XXX somewhat completely buggered; this is in cpu_pmu_context, but we need
> > + * event_pmu_context for rotations. We also need event_pmu_context specific
> > + * scheduling routines. ARGH
> > + *
> > + *  - fixed the cpu_pmu_context vs event_pmu_context thingy
> > + *    (cpu_pmu_context embeds an event_pmu_context)
> > + *
> > + *  - need nr_events/nr_active in epc to do per epc rotation
> > + *    (done)
> > + *
> > + *  - need cpu and task pmu ctx together...
> > + *    (cpc->task_epc)
> > + */
> > +static bool perf_rotate_context(struct perf_cpu_pmu_context *cpc)
> 
> Since it reduces to single cpu context (and single task context) at all times, 
> ideally, it would probably be coded as simple as this: 
> 
> 	perf_rotate_context()
> 	{
>             cpu = this_cpu_ptr(&cpu_context)
>             for_every_pmu(pmu, cpu)

Can't do that, because we have per PMU rotation periods..

>                     for_every_event_ctx(event_ctx, pmu)
> 	                    rotate(event_ctx, pmu)
> 	}

I'm also not sure I get the rest that follows... you only have to rotate
_one_ event per PMU.

I'll try and understand the rest of you email later; brain has checked
out for the day.