Andrew requested this fixup awhile back, and I just now got to it
(apologies for being slow).
To avoid lock contention, we distribute the sched_timer calls across the
cpus so they do not trigger at the same instant. However, I used
NR_CPUS, which can cause needless grouping on small smp systems
depending on your kernel config. This patch converts to using
num_possible_cpus() so we spread it as evenly as possible on every
machine.
Briefly tested w/ NR_CPUS=255 and verified reduced contention.
Signed-off-by: John Stultz <[email protected]>
Index: 2.6-rt/kernel/time/tick-sched.c
===================================================================
--- 2.6-rt.orig/kernel/time/tick-sched.c
+++ 2.6-rt/kernel/time/tick-sched.c
@@ -586,7 +586,7 @@ void tick_setup_sched_timer(void)
/* Get the next period (per cpu) */
ts->sched_timer.expires = tick_init_jiffy_update();
offset = ktime_to_ns(tick_period) >> 1;
- do_div(offset, NR_CPUS);
+ do_div(offset, num_possible_cpus());
offset *= smp_processor_id();
ts->sched_timer.expires = ktime_add_ns(ts->sched_timer.expires, offset);
-
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