linux-kernel - Re: [PATCH 13/14] perf tools: warn on high overhead

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: <87d1hmx7tn.fsf@tassilo.jf.intel.com>
Date:   Wed, 23 Nov 2016 12:25:08 -0800
From:   Andi Kleen <andi@...stfloor.org>
To:     kan.liang@...el.com
Cc:     peterz@...radead.org, mingo@...hat.com, acme@...nel.org,
        linux-kernel@...r.kernel.org, alexander.shishkin@...ux.intel.com,
        tglx@...utronix.de, namhyung@...nel.org, jolsa@...nel.org,
        adrian.hunter@...el.com, wangnan0@...wei.com, mark.rutland@....com
Subject: Re: [PATCH 13/14] perf tools: warn on high overhead

kan.liang@...el.com writes:

> From: Kan Liang <kan.liang@...el.com>
>
> The rough overhead rate can be caculated by the sum of all kinds of
> overhead / elapsed time.
> If the overhead rate is higher than 10%, warning the user.

Thinking about this more: this is comparing the cost of a single
CPU to the total wall clock time. This isn't very good and can
give confusing results with many cores.

Perhaps we need two separate metrics here:

- cost of perf record on its CPU (or later on if it gets multi threaded
  more multiple). Warn if this is >50% or so.
- average perf collection overhead on a CPU. The 10% threshold here
  seems appropiate.

-Andi