[patch 2/2] nohz: change signal tick dependency to wakeup CPUs of member tasks

2020-10-08 Thread Marcelo Tosatti 
Rather than waking up all nohz_full CPUs on the system, only wakeup 
the target CPUs of member threads of the signal.

Reduces interruptions to nohz_full CPUs.

Signed-off-by: Marcelo Tosatti 

Index: linux-2.6/kernel/time/tick-sched.c
===
--- linux-2.6.orig/kernel/time/tick-sched.c
+++ linux-2.6/kernel/time/tick-sched.c
@@ -396,9 +396,17 @@ EXPORT_SYMBOL_GPL(tick_nohz_dep_clear_ta
  * Set a per-taskgroup tick dependency. Posix CPU timers need this in order to 
elapse
  * per process timers.
  */
-void tick_nohz_dep_set_signal(struct signal_struct *sig, enum tick_dep_bits 
bit)
+void tick_nohz_dep_set_signal(struct task_struct *tsk, enum tick_dep_bits bit)
 {
-   tick_nohz_dep_set_all(&sig->tick_dep_mask, bit);
+   int prev;
+   struct task_struct *p;
+
+   prev = atomic_fetch_or(BIT(bit), &tsk->signal->tick_dep_mask);
+   if (!prev) {
+   lockdep_assert_held(&tsk->sighand->siglock);
+   for_each_thread(tsk, p)
+   tick_nohz_kick_task(p);
+   }
 }
 
 void tick_nohz_dep_clear_signal(struct signal_struct *sig, enum tick_dep_bits 
bit)
Index: linux-2.6/include/linux/tick.h
===
--- linux-2.6.orig/include/linux/tick.h
+++ linux-2.6/include/linux/tick.h
@@ -207,7 +207,7 @@ extern void tick_nohz_dep_set_task(struc
   enum tick_dep_bits bit);
 extern void tick_nohz_dep_clear_task(struct task_struct *tsk,
 enum tick_dep_bits bit);
-extern void tick_nohz_dep_set_signal(struct signal_struct *signal,
+extern void tick_nohz_dep_set_signal(struct task_struct *tsk,
 enum tick_dep_bits bit);
 extern void tick_nohz_dep_clear_signal(struct signal_struct *signal,
   enum tick_dep_bits bit);
@@ -252,11 +252,11 @@ static inline void tick_dep_clear_task(s
if (tick_nohz_full_enabled())
tick_nohz_dep_clear_task(tsk, bit);
 }
-static inline void tick_dep_set_signal(struct signal_struct *signal,
+static inline void tick_dep_set_signal(struct task_struct *tsk,
   enum tick_dep_bits bit)
 {
if (tick_nohz_full_enabled())
-   tick_nohz_dep_set_signal(signal, bit);
+   tick_nohz_dep_set_signal(tsk, bit);
 }
 static inline void tick_dep_clear_signal(struct signal_struct *signal,
 enum tick_dep_bits bit)
@@ -284,7 +284,7 @@ static inline void tick_dep_set_task(str
 enum tick_dep_bits bit) { }
 static inline void tick_dep_clear_task(struct task_struct *tsk,
   enum tick_dep_bits bit) { }
-static inline void tick_dep_set_signal(struct signal_struct *signal,
+static inline void tick_dep_set_signal(struct task_struct *tsk,
   enum tick_dep_bits bit) { }
 static inline void tick_dep_clear_signal(struct signal_struct *signal,
 enum tick_dep_bits bit) { }
Index: linux-2.6/kernel/time/posix-cpu-timers.c
===
--- linux-2.6.orig/kernel/time/posix-cpu-timers.c
+++ linux-2.6/kernel/time/posix-cpu-timers.c
@@ -523,7 +523,7 @@ static void arm_timer(struct k_itimer *t
if (CPUCLOCK_PERTHREAD(timer->it_clock))
tick_dep_set_task(p, TICK_DEP_BIT_POSIX_TIMER);
else
-   tick_dep_set_signal(p->signal, TICK_DEP_BIT_POSIX_TIMER);
+   tick_dep_set_signal(p, TICK_DEP_BIT_POSIX_TIMER);
 }
 
 /*
@@ -1358,7 +1358,7 @@ void set_process_cpu_timer(struct task_s
if (*newval < *nextevt)
*nextevt = *newval;
 
-   tick_dep_set_signal(tsk->signal, TICK_DEP_BIT_POSIX_TIMER);
+   tick_dep_set_signal(tsk, TICK_DEP_BIT_POSIX_TIMER);
 }
 
 static int do_cpu_nanosleep(const clockid_t which_clock, int flags,

Re: [patch 2/2] nohz: change signal tick dependency to wakeup CPUs of member tasks

2020-10-08 Thread Marcelo Tosatti 
On Thu, Oct 08, 2020 at 02:35:44PM +0200, Peter Zijlstra wrote:
> On Wed, Oct 07, 2020 at 03:01:53PM -0300, Marcelo Tosatti wrote:
> > Rather than waking up all nohz_full CPUs on the system, only wakeup 
> > the target CPUs of member threads of the signal.
> > 
> > Reduces interruptions to nohz_full CPUs.
> > 
> > Signed-off-by: Marcelo Tosatti 
> > 
> > Index: linux-2.6/kernel/time/tick-sched.c
> > ===
> > --- linux-2.6.orig/kernel/time/tick-sched.c
> > +++ linux-2.6/kernel/time/tick-sched.c
> > @@ -398,7 +398,15 @@ EXPORT_SYMBOL_GPL(tick_nohz_dep_clear_ta
> >   */
> >  void tick_nohz_dep_set_signal(struct signal_struct *sig, enum 
> > tick_dep_bits bit)
> >  {
> > -   tick_nohz_dep_set_all(&sig->tick_dep_mask, bit);
> > +   int prev;
> > +
> > +   prev = atomic_fetch_or(BIT(bit), &sig->tick_dep_mask);
> > +   if (!prev) {
> > +   rcu_read_lock();
> > +   for_each_thread(sig, t)
> > +   tick_nohz_kick_task(t);
> > +   rcu_read_unlock();
> > +   }
> >  }
> 
> AFAICT, and this makes perfect sense, this function is only ever used
> while holding sighand->siglock, which makes the RCU read lock
> superfluous.
> 
> Would it make sense to change the signal_struct argument to task_struct,
> such that we can write:
> 
>   lockdep_assert_held(&p->sighand->siglock);
>   for_each_thread(p->signal, t)
>   tick_nohz_kick_task(t);
> 
> ?

Makes sense, resending -v3.

Re: [patch 2/2] nohz: change signal tick dependency to wakeup CPUs of member tasks

2020-10-08 Thread Peter Zijlstra 
On Wed, Oct 07, 2020 at 03:01:53PM -0300, Marcelo Tosatti wrote:
> Rather than waking up all nohz_full CPUs on the system, only wakeup 
> the target CPUs of member threads of the signal.
> 
> Reduces interruptions to nohz_full CPUs.
> 
> Signed-off-by: Marcelo Tosatti 
> 
> Index: linux-2.6/kernel/time/tick-sched.c
> ===
> --- linux-2.6.orig/kernel/time/tick-sched.c
> +++ linux-2.6/kernel/time/tick-sched.c
> @@ -398,7 +398,15 @@ EXPORT_SYMBOL_GPL(tick_nohz_dep_clear_ta
>   */
>  void tick_nohz_dep_set_signal(struct signal_struct *sig, enum tick_dep_bits 
> bit)
>  {
> - tick_nohz_dep_set_all(&sig->tick_dep_mask, bit);
> + int prev;
> +
> + prev = atomic_fetch_or(BIT(bit), &sig->tick_dep_mask);
> + if (!prev) {
> + rcu_read_lock();
> + for_each_thread(sig, t)
> + tick_nohz_kick_task(t);
> + rcu_read_unlock();
> + }
>  }

AFAICT, and this makes perfect sense, this function is only ever used
while holding sighand->siglock, which makes the RCU read lock
superfluous.

Would it make sense to change the signal_struct argument to task_struct,
such that we can write:

lockdep_assert_held(&p->sighand->siglock);
for_each_thread(p->signal, t)
tick_nohz_kick_task(t);

?

[patch 2/2] nohz: change signal tick dependency to wakeup CPUs of member tasks

2020-10-07 Thread Marcelo Tosatti 
Rather than waking up all nohz_full CPUs on the system, only wakeup 
the target CPUs of member threads of the signal.

Reduces interruptions to nohz_full CPUs.

Signed-off-by: Marcelo Tosatti 

Index: linux-2.6/kernel/time/tick-sched.c
===
--- linux-2.6.orig/kernel/time/tick-sched.c
+++ linux-2.6/kernel/time/tick-sched.c
@@ -398,7 +398,15 @@ EXPORT_SYMBOL_GPL(tick_nohz_dep_clear_ta
  */
 void tick_nohz_dep_set_signal(struct signal_struct *sig, enum tick_dep_bits 
bit)
 {
-   tick_nohz_dep_set_all(&sig->tick_dep_mask, bit);
+   int prev;
+
+   prev = atomic_fetch_or(BIT(bit), &sig->tick_dep_mask);
+   if (!prev) {
+   rcu_read_lock();
+   for_each_thread(sig, t)
+   tick_nohz_kick_task(t);
+   rcu_read_unlock();
+   }
 }
 
 void tick_nohz_dep_clear_signal(struct signal_struct *sig, enum tick_dep_bits 
bit)