From: Namhyung Kim <namhyung@kernel.org>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>,
LKML <linux-kernel@vger.kernel.org>,
Adrian Hunter <adrian.hunter@intel.com>,
David Ahern <dsahern@gmail.com>, Ingo Molnar <mingo@kernel.org>,
Jiri Olsa <jolsa@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Stephane Eranian <eranian@google.com>
Subject: Re: [PATCH 2/3] perf tools: Spare double comparison of callchain first entry
Date: Wed, 15 Jan 2014 15:23:46 +0900 [thread overview]
Message-ID: <87y52h930t.fsf@sejong.aot.lge.com> (raw)
In-Reply-To: <1389713836-13375-3-git-send-email-fweisbec@gmail.com> (Frederic Weisbecker's message of "Tue, 14 Jan 2014 16:37:15 +0100")
On Tue, 14 Jan 2014 16:37:15 +0100, Frederic Weisbecker wrote:
> When a new callchain child branch matches an existing one in the rbtree,
> the comparison of its first entry is performed twice:
>
> 1) From append_chain_children() on branch lookup
>
> 2) If 1) reports a match, append_chain() then compares all entries of
> the new branch against the matching node in the rbtree, and this
> comparison includes the first entry of the new branch again.
Right.
>
> Lets shortcut this by performing the whole comparison only from
> append_chain() which then returns the result of the comparison between
> the first entry of the new branch and the iterating node in the rbtree.
> If the first entry matches, the lookup on the current level of siblings
> stops and propagates to the children of the matching nodes.
Hmm.. it looks like that I thought directly calling append_chain() has
some overhead - but it's not.
>
> This results in less comparisons performed by the CPU.
Do you have any numbers? I suspect it'd not be a big change, but just
curious.
>
> Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Reviewed-by: Namhyung Kim <namhyung@kernel.org>
Thanks,
Namhyung
next prev parent reply other threads:[~2014-01-15 6:24 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-14 15:37 perf tools: Random cleanups Frederic Weisbecker
2014-01-14 15:37 ` [PATCH 1/3] perf tools: Do proper comm override error handling Frederic Weisbecker
2014-01-15 5:54 ` Namhyung Kim
2014-01-19 12:25 ` [tip:perf/core] " tip-bot for Frederic Weisbecker
2014-01-14 15:37 ` [PATCH 2/3] perf tools: Spare double comparison of callchain first entry Frederic Weisbecker
2014-01-15 6:23 ` Namhyung Kim [this message]
2014-01-15 16:59 ` Frederic Weisbecker
2014-01-16 1:17 ` Namhyung Kim
2014-01-16 17:34 ` Frederic Weisbecker
2014-01-16 19:47 ` Arnaldo Carvalho de Melo
2014-01-17 7:56 ` Namhyung Kim
2014-01-17 16:07 ` Frederic Weisbecker
2014-01-19 12:25 ` [tip:perf/core] perf callchain: " tip-bot for Frederic Weisbecker
2014-01-14 15:37 ` [PATCH 3/3] perf tools: Remove unnecessary callchain cursor state restore on unmatch Frederic Weisbecker
2014-01-15 6:24 ` Namhyung Kim
2014-01-19 12:25 ` [tip:perf/core] " tip-bot for Frederic Weisbecker
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