Messages in this thread | | | From | Kevin Hilman <> | Subject | Re: [PATCH 1/2] sched/nohz: add debugfs control over sched_tick_max_deferment | Date | Mon, 06 Jan 2014 10:37:27 -0800 |
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Frederic Weisbecker <fweisbec@gmail.com> writes:
> On Tue, Dec 17, 2013 at 01:23:07PM -0800, Kevin Hilman wrote: >> Allow debugfs override of sched_tick_max_deferment in order to ease >> finding/fixing the remaining issues with full nohz. >> >> The value to be written is in jiffies, and -1 means the max deferment >> is disabled (scheduler_tick_max_deferment() returns KTIME_MAX.) >> >> Cc: Frederic Weisbecker <fweisbec@gmail.com> >> Signed-off-by: Kevin Hilman <khilman@linaro.org> >> --- >> kernel/sched/core.c | 16 +++++++++++++++- >> 1 file changed, 15 insertions(+), 1 deletion(-) >> >> diff --git a/kernel/sched/core.c b/kernel/sched/core.c >> index 5ac63c9a995a..4b1fe3e69fe4 100644 >> --- a/kernel/sched/core.c >> +++ b/kernel/sched/core.c >> @@ -2175,6 +2175,8 @@ void scheduler_tick(void) >> } >> >> #ifdef CONFIG_NO_HZ_FULL >> +static u32 sched_tick_max_deferment = HZ; >> + >> /** >> * scheduler_tick_max_deferment >> * >> @@ -2193,13 +2195,25 @@ u64 scheduler_tick_max_deferment(void) >> struct rq *rq = this_rq(); >> unsigned long next, now = ACCESS_ONCE(jiffies); >> >> - next = rq->last_sched_tick + HZ; >> + if (sched_tick_max_deferment == -1) >> + return KTIME_MAX; >> + >> + next = rq->last_sched_tick + sched_tick_max_deferment; >> >> if (time_before_eq(next, now)) >> return 0; >> >> return jiffies_to_usecs(next - now) * NSEC_PER_USEC; >> } >> + >> +static __init int sched_nohz_full_init_debug(void) >> +{ >> + debugfs_create_u32("sched_tick_max_deferment", 0644, NULL, >> + &sched_tick_max_deferment); >> + >> + return 0; >> +} >> +late_initcall(sched_nohz_full_init_debug); > > If the goal is mostly to turn off sched_tick_max_deferment (set to -1), we should > perhaps make it a boolean sched feature (see kernel/sched/features.h) as it's a pretty > well consolidated interface.
Well, I suspect folks may want to set it to various values, depending on workload to experiment with the results.
Also, my first attempt was to add control over this via sysctl[1] (though not sched_features) and you suggested[2] I use debugfs instead since this should be a temporary hack until we can remove the 1Hz residual tick.
Kevin
[1] http://marc.info/?l=linux-kernel&m=137159992306877&w=2 [2] http://marc.info/?l=linux-kernel&m=137166737830821&w=2
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