linux-kernel - Re: [RFC][PATCH] perf: Rewrite core context handling

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Message-ID: <20181017110651.GI3121@hirez.programming.kicks-ass.net>
Date:   Wed, 17 Oct 2018 13:06:51 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Song Liu <songliubraving@...com>
Cc:     Alexey Budankov <alexey.budankov@...ux.intel.com>,
        Ingo Molnar <mingo@...nel.org>,
        lkml <linux-kernel@...r.kernel.org>,
        "acme@...nel.org" <acme@...nel.org>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Jiri Olsa <jolsa@...hat.com>,
        Stephane Eranian <eranian@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "megha.dey@...el.com" <megha.dey@...el.com>,
        "frederic@...nel.org" <frederic@...nel.org>
Subject: Re: [RFC][PATCH] perf: Rewrite core context handling

On Tue, Oct 16, 2018 at 06:28:10PM +0000, Song Liu wrote:
> > How about this: 
> > 
> > 1. Keep multiple perf_cpu_context per CPU, just like before this patch. 
> > 
> > 2. For perf_event_context, add PMU as an order for the RB tree. 
> > 
> > 3. (hw) pmu->perf_cpu_context->ctx only has events for this PMU (and sw 
> >   events moved to this context).
> > 
> > 4. task->perf_event_ctxp has events for all PMUs. 
> > 
> > With this path, we keep the existing perf_cpu_context/perf_event_context
> > logic as-is, which I think is simp.ler than the new logic (with extra
> > *_pmu_context). And it should also solve the problem. 
> > 
> > Does this make sense? If this doesn't look too broken, I am happy to
> > draft RFC for it. 
> > 
> 
> I am not sure whether you missed this one, or found it totally insane. 
> Could you please share your comments on it? My gut feeling is that this 
> would be a simpler patch to solve the problem (two hw PMUs). (It might 
> be less efficient though). 

Ah, sorry, somehow this email got lost.

That makes task and cpu contexts wildly different, which will complicate
matters I feel.