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

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Message-ID: <20160705125226.GE20478@leverpostej>
Date:	Tue, 5 Jul 2016 13:52:27 +0100
From:	Mark Rutland <mark.rutland@....com>
To:	Peter Zijlstra <peterz@...radead.org>
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, Jul 05, 2016 at 02:04:26PM +0200, Peter Zijlstra wrote:
> On Tue, Jul 05, 2016 at 10:44:48AM +0100, Mark Rutland wrote:
> > My bad; I assumed that for both PMUs we'd start at the root, and thus
> > would need to re-sort in order to get the current CPU's PMU ordered
> > first, much like currently with rotation.
> > 
> > I guess I'm having difficulty figuring out the structure of that tree.
> > If we can easily/cheaply find the relevant sub-tree then the above isn't
> > an issue.
> 
> struct event {
> 	struct rb_node node;
> 	int pmu_id;
> 	s64 lag;
> 	...
> };
> 
> bool event_less(struct rb_node *a, struct rb_node *b)
> {
> 	struct event *left = rb_entry(a, struct event, node);
> 	struct event *right = rb_entry(b, struct event, node);
> 
> 	if (a->pmu_id < b->pmu_id)
> 		return true;
> 
> 	if (b->pmu_id > a->pmu_id)
> 		return false;
> 
> 	/* a->pmu_id == b->pmu_id */
> 	if (a->lag < b->lag)
> 		return true;
> 
> 	return false;
> }
> 
> Will give you a tree with primary order @pmu_id and secondary order
> @lag.
> 
> Which you'd iterate like:
> 
> 	for (event = event_find(pmu_id); event->pmu_id == pmu_id; event = event_next(event)) {
> 	}
> 
> And get only the events matching @pmu_id in @lag order.

Cheers! Sorry for being thick; I think I understand now.

I'll have a tinker with the idea.

Thanks,
Mark.