linux-kernel - [PATCH 0/3] reduce nohz_full syscall overhead by 10%

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Date:	Thu, 30 Apr 2015 17:23:52 -0400
From:	riel@...hat.com
To:	linux-kernel@...r.kernel.org
Cc:	x86@...nel.org, williams@...hat.com, luto@...nel.org,
	mingo@...nel.org, bonzini@...hat.com, fweisbec@...hat.com,
	peterz@...radead.org, heiko.carstens@...ibm.com, tglx@...utronix.de
Subject: [PATCH 0/3] reduce nohz_full syscall overhead by 10%

Profiling reveals that a lot of the overhead from the nohz_full
accounting seems to come not from the accounting itself, but from
disabling and re-enabling interrupts.

This patch series removes the interrupt disabling & re-enabling
from __acct_update_integrals, which is called on both syscall
entry and exit, as well as from the user_exit called on syscall
entry.

Together they speed up a benchmark that calls getpriority in
a row 10 million times by about 10%:

		run time	system time
vanilla		5.49s		2.08s
__acct patch	5.21s		1.92s
both patches	4.88s		1.71s

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