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authorMike Galbraith <mgalbraith@suse.de>2012-05-08 14:20:58 +0400
committerThomas Gleixner <tglx@linutronix.de>2012-05-25 03:44:50 +0400
commit5307c9556bc17e3cd26d4e94fc3b2565921834de (patch)
treee51937060ccd5e293dec7246a7961b0ae5509a53 /include/linux/clockchips.h
parentce004178be1bbaa292e9e6497939e2970300095a (diff)
downloadlinux-5307c9556bc17e3cd26d4e94fc3b2565921834de.tar.xz
tick: Add tick skew boot option
Let the user decide whether power consumption or jitter is the more important consideration for their machines. Quoting removal commit af5ab277ded04bd9bc6b048c5a2f0e7d70ef0867: "Historically, Linux has tried to make the regular timer tick on the various CPUs not happen at the same time, to avoid contention on xtime_lock. Nowadays, with the tickless kernel, this contention no longer happens since time keeping and updating are done differently. In addition, this skew is actually hurting power consumption in a measurable way on many-core systems." Problems: - Contrary to the above, systems do encounter contention on both xtime_lock and RCU structure locks when the tick is synchronized. - Moderate sized RT systems suffer intolerable jitter due to the tick being synchronized. - SGI reports the same for their large systems. - Fully utilized systems reap no power saving benefit from skew removal, but do suffer from resulting induced lock contention. - 0209f649 rcu: limit rcu_node leaf-level fanout This patch was born to combat lock contention which testing showed to have been _induced by_ skew removal. Skew the tick, contention disappeared virtually completely. Signed-off-by: Mike Galbraith <mgalbraith@suse.de> Link: http://lkml.kernel.org/r/1336472458.21924.78.camel@marge.simpson.net Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Diffstat (limited to 'include/linux/clockchips.h')
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