diff options
Diffstat (limited to 'patches/0004-tick-Add-tick-skew-boot-option.patch')
| -rw-r--r-- | patches/0004-tick-Add-tick-skew-boot-option.patch | 106 |
1 files changed, 106 insertions, 0 deletions
diff --git a/patches/0004-tick-Add-tick-skew-boot-option.patch b/patches/0004-tick-Add-tick-skew-boot-option.patch new file mode 100644 index 0000000..995edce --- /dev/null +++ b/patches/0004-tick-Add-tick-skew-boot-option.patch @@ -0,0 +1,106 @@ +From bf48ba64a0969750c739692a2ce24ba9ba05c29e Mon Sep 17 00:00:00 2001 +From: Mike Galbraith <mgalbraith@suse.de> +Date: Tue, 8 May 2012 12:20:58 +0200 +Subject: [PATCH 004/254] 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. + +[ tglx: build fix ] + +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> +--- + Documentation/kernel-parameters.txt | 9 +++++++++ + kernel/time/tick-sched.c | 18 ++++++++++++++++++ + 2 files changed, 27 insertions(+) + +diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt +index c1601e5..1e0150e 100644 +--- a/Documentation/kernel-parameters.txt ++++ b/Documentation/kernel-parameters.txt +@@ -2426,6 +2426,15 @@ 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 +diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c +index 6a3a5b9..efd3866 100644 +--- a/kernel/time/tick-sched.c ++++ b/kernel/time/tick-sched.c +@@ -814,6 +814,16 @@ static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer) + return HRTIMER_RESTART; + } + ++static int sched_skew_tick; ++ ++static int __init skew_tick(char *str) ++{ ++ get_option(&str, &sched_skew_tick); ++ ++ return 0; ++} ++early_param("skew_tick", skew_tick); ++ + /** + * tick_setup_sched_timer - setup the tick emulation timer + */ +@@ -831,6 +841,14 @@ void tick_setup_sched_timer(void) + /* Get the next period (per cpu) */ + hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update()); + ++ /* Offset the tick to avert xtime_lock contention. */ ++ if (sched_skew_tick) { ++ u64 offset = ktime_to_ns(tick_period) >> 1; ++ do_div(offset, num_possible_cpus()); ++ offset *= smp_processor_id(); ++ hrtimer_add_expires_ns(&ts->sched_timer, offset); ++ } ++ + for (;;) { + hrtimer_forward(&ts->sched_timer, now, tick_period); + hrtimer_start_expires(&ts->sched_timer, +-- +1.7.10.4 + |