linux-kernel - Re: [PATCH 2/3] perf tools: Spare double comparison of callchain first entry

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <87y52h930t.fsf@sejong.aot.lge.com>
Date:	Wed, 15 Jan 2014 15:23:46 +0900
From:	Namhyung Kim <namhyung@...nel.org>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Arnaldo Carvalho de Melo <acme@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	David Ahern <dsahern@...il.com>,
	Ingo Molnar <mingo@...nel.org>, Jiri Olsa <jolsa@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Stephane Eranian <eranian@...gle.com>
Subject: Re: [PATCH 2/3] perf tools: Spare double comparison of callchain first entry

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@...il.com>

Reviewed-by: Namhyung Kim <namhyung@...nel.org>

Thanks,
Namhyung
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/