linux-kernel - Re: [PATCH v6 1/3] perf/core: use rb trees for pinned/flexible groups

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Message-ID: <87lgm2xz0m.fsf@ashishki-desk.ger.corp.intel.com>
Date:   Tue, 29 Aug 2017 16:51:53 +0300
From:   Alexander Shishkin <alexander.shishkin@...ux.intel.com>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Kan Liang <kan.liang@...el.com>,
        Dmitri Prokhorov <Dmitry.Prohorov@...el.com>,
        Valery Cherepennikov <valery.cherepennikov@...el.com>,
        Mark Rutland <mark.rutland@....com>,
        Stephane Eranian <eranian@...gle.com>,
        David Carrillo-Cisneros <davidcc@...gle.com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6 1/3] perf/core: use rb trees for pinned/flexible groups

Alexey Budankov <alexey.budankov@...ux.intel.com> writes:

> Now I figured that not all indexed events are always located under 
> the root with the same cpu, and it depends on the order of insertion
> e.g. with insertion order 01,02,03,14,15,16 we get this:
>
>      02
>     /  \
>    01  14
>       /  \
>      03  15
>            \
>            16
>
> and it is unclear how to iterate cpu==0 part of tree in this case.

Using this example, rb_next() should take you through the nodes in this
order (assuming you start with 01): 01, 02, 03, 14, etc. So you iterate
while event->cpu==cpu using rb_next() and you should be fine.

> Iterating cpu specific subtree like this:
>
> #define for_each_group_event(event, group, cpu, pmu, field)	 \
> 	for (event = rb_entry_safe(group_first(group, cpu, pmu), \
> 				   typeof(*event), field);	 \
> 	     event && event->cpu == cpu && event->pmu == pmu;	 \
> 	     event = rb_entry_safe(rb_next(&event->field),	 \
> 				   typeof(*event), field))

Afaict, this assumes that you are also ordering on event->pmu, which
should be reflected in your _less function. And also assuming that
group_first() is doing the right thing. Can we see the code?

Regards,
--
Alex