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