linux-kernel - Re: [PATCH] perf: fix pmu::filter

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Date:	Tue, 5 Jul 2016 10:35:26 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mark Rutland <mark.rutland@....com>
Cc:	linux-kernel@...r.kernel.org,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Will Deacon <will.deacon@....com>
Subject: Re: [PATCH] perf: fix pmu::filter_match for SW-led groups

On Mon, Jul 04, 2016 at 07:05:35PM +0100, Mark Rutland wrote:
> On Sat, Jul 02, 2016 at 06:40:25PM +0200, Peter Zijlstra wrote:
> > One of the ways I was looking at getting that done is a virtual runtime
> > scheduler (just like cfs). The tricky point is merging two virtual
> > runtime trees. But I think that should be doable if we sort the trees on
> > lag.
> > 
> > In any case, the relevance to your question is that once we have a tree,
> > we can play games with order; that is, if we first order on PMU-id and
> > only second on lag, we get whole subtree clusters specific for a PMU.
> 
> Hmm... I'm not sure how that helps in this case. Wouldn't we still need
> to walk the sibling list to get the HW PMU-id in the case of a SW group
> leader?

Since there is a hardware even in the group, it must be part of the
hardware pmu list/tree and would thus end up classified (and sorted) by
that (hardware) PMU-id.

> For the heterogeenous case we'd need a different sort order per-cpu
> (well, per microarchitecture), which sounds like we're going to have to
> fully sort the events every time they move between CPUs. :/

Confused, I thought that for the HG case you had multiple events, one
for each PMU. If we classify these events differently we'd simply use a
different subtree depending on which CPU the task lands.

Currently we've munged the two PMUs together, because, well, that's the
only way.

> I also had another though about solving the SW-led group case: if the
> leader had a reference to the group's HW PMU (of which there should only
> be one), we can filter on that alone, and can also use that in
> group_sched_in rather than the ctx->pmu, avoiding the issue that
> ctx->pmu is not the same as the group's HW PMU.
> 
> I'll have a play with that approach in the mean time.

Right, adds one more pointer to the struct event, but that thing is
massive already.