linux-kernel - [RFC 0/4] do not make cputime scaling in kernel

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Message-Id: <1364489605-5443-1-git-send-email-sgruszka@redhat.com>
Date:	Thu, 28 Mar 2013 17:53:21 +0100
From:	Stanislaw Gruszka <sgruszka@...hat.com>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>, hpa@...or.com,
	rostedt@...dmis.org, akpm@...ux-foundation.org, tglx@...utronix.de,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: [RFC 0/4] do not make cputime scaling in kernel

This patch series removes cputime scaling from kernel. It can be easily
done in user space using floating point if we provide sum_exec_runtime,
what patches 2/4 and 3/4 do. I have procps which utilize that:

http://people.redhat.com/sgruszka/procps-use-sum_exec_runtime.patch

I will post it, if this patch set will be queued.

Change affect also getrusage() and times() syscals, but I don't think
kernel give guarantees about utime/stime precision, in a matter of fact
before commit b27f03d4bdc145a09fb7b0c0e004b29f1ee555fa, we do not
perform any scaling and we provided raw cputime values to user space.

Providing sum_exec_runtime via proc is done against malware that utilize
lot of cpu time but hide itself from top program.

This affect kernels not compiled with CONFIG_VIRT_CPU_ACCOUNTING_{GEN,NATIVE},
if user choose to compile kernel with some of those options, he/she will
have more precise cputime accounting, what is documented in Kconfig.

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