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authorMike Galbraith <mgalbraith@suse.de>2012-05-08 12:20:58 +0200
committerThomas Gleixner <tglx@linutronix.de>2012-05-25 01:44:50 +0200
commit5307c9556bc17e3cd26d4e94fc3b2565921834de (patch)
treee51937060ccd5e293dec7246a7961b0ae5509a53 /Documentation/kernel-parameters.txt
parentce004178be1bbaa292e9e6497939e2970300095a (diff)
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op-kernel-dev-5307c9556bc17e3cd26d4e94fc3b2565921834de.tar.gz
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 'Documentation/kernel-parameters.txt')
-rw-r--r--Documentation/kernel-parameters.txt9
1 files changed, 9 insertions, 0 deletions
diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index b69cfdc12..ea38cd1 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2532,6 +2532,15 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
sched_debug [KNL] Enables verbose scheduler debug messages.
+ skew_tick= [KNL] Offset the periodic timer tick per cpu to mitigate
+ xtime_lock contention on larger systems, and/or RCU lock
+ contention on all systems with CONFIG_MAXSMP set.
+ Format: { "0" | "1" }
+ 0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
+ 1 -- enable.
+ Note: increases power consumption, thus should only be
+ enabled if running jitter sensitive (HPC/RT) workloads.
+
security= [SECURITY] Choose a security module to enable at boot.
If this boot parameter is not specified, only the first
security module asking for security registration will be
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