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

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Date:	Sat, 2 Jul 2016 18:40:25 +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 Tue, Jun 14, 2016 at 04:10:41PM +0100, Mark Rutland wrote:
> However, pmu::filter_match is only called for the leader of each event
> group. When the leader is a SW event, we do not filter the groups, and
> may fail at pmu::add time, and when this happens we'll give up on
> scheduling any event groups later in the list until they are rotated
> ahead of the failing group.

Ha! indeed.

> I've tried to find a better way of handling this (without needing to walk the
> siblings list), but so far I'm at a loss. At least it's "only" O(n) in the size
> of the sibling list we were going to walk anyway.
> 
> I suspect that at a more fundamental level, I need to stop sharing a
> perf_hw_context between HW PMUs (i.e. replace task_struct::perf_event_ctxp with
> something that can handle multiple HW PMUs). From previous attempts I'm not
> sure if that's going to be possible.
> 
> Any ideas appreciated!

So I think I have half-cooked ideas.

One of the problems I've been wanting to solve for a long time is that
the per-cpu flexible list has priority over the per-task flexible list.

I would like them to rotate together.

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.

Lost of details missing in that picture, but I think something along
those lines might get us what we want.