itimers: remove the per-cpu-ish-ness

Either we bounce once cacheline per cpu per tick, yielding n^2 bounces
or we just bounce a single..

Also, using per-cpu allocations for the thread-groups complicates the
per-cpu allocator in that its currently aimed to be a fixed sized
allocator and the only possible extention to that would be vmap based,
which is seriously constrained on 32 bit archs.

So making the per-cpu memory requirement depend on the number of
processes is an issue.

Lastly, it didn't deal with cpu-hotplug, although admittedly that might
be fixable.

Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

1 files changed, 15 insertions, 18 deletions

diff --git a/kernel/sched_stats.h b/kernel/sched_stats.h
index f2773b5d1226..8ab0cef8ecab 100644
--- a/kernel/sched_stats.h
+++ b/kernel/sched_stats.h
@@ -296,6 +296,7 @@ sched_info_switch(struct task_struct *prev, struct task_struct *next)
 static inline void account_group_user_time(struct task_struct *tsk,
                                            cputime_t cputime)
 {
+        struct task_cputime *times;
         struct signal_struct *sig;
 
         /* tsk == current, ensure it is safe to use ->signal */
@@ -303,13 +304,11 @@ static inline void account_group_user_time(struct task_struct *tsk,
                 return;
 
         sig = tsk->signal;
-        if (sig->cputime.totals) {
-                struct task_cputime *times;
+        times = &sig->cputime.totals;
 
-                times = per_cpu_ptr(sig->cputime.totals, get_cpu());
-                times->utime = cputime_add(times->utime, cputime);
-                put_cpu_no_resched();
-        }
+        spin_lock(&times->lock);
+        times->utime = cputime_add(times->utime, cputime);
+        spin_unlock(&times->lock);
 }
 
 /**
@@ -325,6 +324,7 @@ static inline void account_group_user_time(struct task_struct *tsk,
 static inline void account_group_system_time(struct task_struct *tsk,
                                              cputime_t cputime)
 {
+        struct task_cputime *times;
         struct signal_struct *sig;
 
         /* tsk == current, ensure it is safe to use ->signal */
@@ -332,13 +332,11 @@ static inline void account_group_system_time(struct task_struct *tsk,
                 return;
 
         sig = tsk->signal;
-        if (sig->cputime.totals) {
-                struct task_cputime *times;
+        times = &sig->cputime.totals;
 
-                times = per_cpu_ptr(sig->cputime.totals, get_cpu());
-                times->stime = cputime_add(times->stime, cputime);
-                put_cpu_no_resched();
-        }
+        spin_lock(&times->lock);
+        times->stime = cputime_add(times->stime, cputime);
+        spin_unlock(&times->lock);
 }
 
 /**
@@ -354,6 +352,7 @@ static inline void account_group_system_time(struct task_struct *tsk,
 static inline void account_group_exec_runtime(struct task_struct *tsk,
                                               unsigned long long ns)
 {
+        struct task_cputime *times;
         struct signal_struct *sig;
 
         sig = tsk->signal;
@@ -362,11 +361,9 @@ static inline void account_group_exec_runtime(struct task_struct *tsk,
         if (unlikely(!sig))
                 return;
 
-        if (sig->cputime.totals) {
-                struct task_cputime *times;
+        times = &sig->cputime.totals;
 
-                times = per_cpu_ptr(sig->cputime.totals, get_cpu());
-                times->sum_exec_runtime += ns;
-                put_cpu_no_resched();
-        }
+        spin_lock(&times->lock);
+        times->sum_exec_runtime += ns;
+        spin_unlock(&times->lock);
 }