| Message ID | 1411760732-14102-1-git-send-email-khilman@kernel.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hi Frederic, On Fri, Sep 26, 2014 at 12:45 PM, Kevin Hilman <khilman@kernel.org> wrote: > From: Kevin Hilman <khilman@linaro.org> > > 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> This is just an attempt to revive and hopefully finalize the discussion started a while back[1]. Kevin [1] https://lkml.org/lkml/2014/1/14/914
On Fri, Sep 26, 2014 at 12:45:32PM -0700, Kevin Hilman wrote: > From: Kevin Hilman <khilman@linaro.org> > > 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> So, I'm worried that it becomes a hack that everybody uses to shutdown the tick completely then nobody will come and fix the issue that prevents from doing it properly. I seriously doubt this will be used for development purpose to help fixing the real problem. Quite the opposite. If developers want to do testing, they can as well comment out the call to scheduler_max_tick_deferment(). > --- > 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 bc1638b33449..dee044a5d447 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -2514,6 +2514,8 @@ void scheduler_tick(void) > } > > #ifdef CONFIG_NO_HZ_FULL > +static u32 sched_tick_max_deferment = HZ; > + > /** > * scheduler_tick_max_deferment > * > @@ -2532,13 +2534,25 @@ 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_nsecs(next - now); > } > + > +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); > #endif > > notrace unsigned long get_parent_ip(unsigned long addr) > -- > 2.1.0 >
Frederic Weisbecker <fweisbec@gmail.com> writes: > On Fri, Sep 26, 2014 at 12:45:32PM -0700, Kevin Hilman wrote: >> From: Kevin Hilman <khilman@linaro.org> >> >> 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> > > So, I'm worried that it becomes a hack that everybody uses to shutdown > the tick completely then nobody will come and fix the issue that prevents > from doing it properly. OK. > I seriously doubt this will be used for development purpose to help > fixing the real problem. Well, that's what I was using it for, until I was distracted by other tasks. > Quite the opposite. If developers want to do > testing, they can as well comment out the call to scheduler_max_tick_deferment(). OK, fair enough. Thanks, Kevin
diff --git a/kernel/sched/core.c b/kernel/sched/core.c index bc1638b33449..dee044a5d447 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -2514,6 +2514,8 @@ void scheduler_tick(void) } #ifdef CONFIG_NO_HZ_FULL +static u32 sched_tick_max_deferment = HZ; + /** * scheduler_tick_max_deferment * @@ -2532,13 +2534,25 @@ 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_nsecs(next - now); } + +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); #endif notrace unsigned long get_parent_ip(unsigned long addr)