[PATCH 2/2] sched,time: call __acct_update_integrals once a jiffy

From: riel
Date: Fri Jan 29 2016 - 17:40:50 EST


From: Rik van Riel <riel@xxxxxxxxxx>

Because __acct_update_integrals does nothing unless the time
interval in question exceeds a jiffy, there is no real reason
to call it more than once a jiffy from the syscall, irq, and
guest entry & exit paths.

If tasks get rescheduled frequently, the scheduler will still
update their time statistics normally. This patch only impacts
longer running tasks.

This speeds up

Signed-off-by: Rik van Riel <riel@xxxxxxxxxx>
---
include/linux/sched.h | 1 +
kernel/sched/cputime.c | 35 +++++++++++++++++++++++++++++------
2 files changed, 30 insertions(+), 6 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index a10494a94cc3..019c3af98503 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1532,6 +1532,7 @@ struct task_struct {
struct prev_cputime prev_cputime;
#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
seqcount_t vtime_seqcount;
+ unsigned long vtime_jiffies;
unsigned long long vtime_snap;
enum {
/* Task is sleeping or running in a CPU with VTIME inactive */
diff --git a/kernel/sched/cputime.c b/kernel/sched/cputime.c
index b2ab2ffb1adc..923c110319b1 100644
--- a/kernel/sched/cputime.c
+++ b/kernel/sched/cputime.c
@@ -668,6 +668,15 @@ void thread_group_cputime_adjusted(struct task_struct *p, cputime_t *ut, cputime
#endif /* !CONFIG_VIRT_CPU_ACCOUNTING_NATIVE */

#ifdef CONFIG_VIRT_CPU_ACCOUNTING_GEN
+static bool vtime_jiffies_changed(struct task_struct *tsk, unsigned long now)
+{
+ if (tsk->vtime_jiffies == jiffies)
+ return false;
+
+ tsk->vtime_jiffies = jiffies;
+ return true;
+}
+
static unsigned long long vtime_delta(struct task_struct *tsk)
{
unsigned long long clock;
@@ -699,6 +708,9 @@ static void __vtime_account_system(struct task_struct *tsk)

void vtime_account_system(struct task_struct *tsk)
{
+ if (!vtime_jiffies_changed(tsk, jiffies))
+ return;
+
write_seqcount_begin(&tsk->vtime_seqcount);
__vtime_account_system(tsk);
write_seqcount_end(&tsk->vtime_seqcount);
@@ -707,7 +719,8 @@ void vtime_account_system(struct task_struct *tsk)
void vtime_gen_account_irq_exit(struct task_struct *tsk)
{
write_seqcount_begin(&tsk->vtime_seqcount);
- __vtime_account_system(tsk);
+ if (vtime_jiffies_changed(tsk, jiffies))
+ __vtime_account_system(tsk);
if (context_tracking_in_user())
tsk->vtime_snap_whence = VTIME_USER;
write_seqcount_end(&tsk->vtime_seqcount);
@@ -718,16 +731,19 @@ void vtime_account_user(struct task_struct *tsk)
cputime_t delta_cpu;

write_seqcount_begin(&tsk->vtime_seqcount);
- delta_cpu = get_vtime_delta(tsk);
tsk->vtime_snap_whence = VTIME_SYS;
- account_user_time(tsk, delta_cpu, cputime_to_scaled(delta_cpu));
+ if (vtime_jiffies_changed(tsk, jiffies)) {
+ delta_cpu = get_vtime_delta(tsk);
+ account_user_time(tsk, delta_cpu, cputime_to_scaled(delta_cpu));
+ }
write_seqcount_end(&tsk->vtime_seqcount);
}

void vtime_user_enter(struct task_struct *tsk)
{
write_seqcount_begin(&tsk->vtime_seqcount);
- __vtime_account_system(tsk);
+ if (vtime_jiffies_changed(tsk, jiffies))
+ __vtime_account_system(tsk);
tsk->vtime_snap_whence = VTIME_USER;
write_seqcount_end(&tsk->vtime_seqcount);
}
@@ -742,7 +758,8 @@ void vtime_guest_enter(struct task_struct *tsk)
* that can thus safely catch up with a tickless delta.
*/
write_seqcount_begin(&tsk->vtime_seqcount);
- __vtime_account_system(tsk);
+ if (vtime_jiffies_changed(tsk, jiffies))
+ __vtime_account_system(tsk);
current->flags |= PF_VCPU;
write_seqcount_end(&tsk->vtime_seqcount);
}
@@ -759,8 +776,12 @@ EXPORT_SYMBOL_GPL(vtime_guest_exit);

void vtime_account_idle(struct task_struct *tsk)
{
- cputime_t delta_cpu = get_vtime_delta(tsk);
+ cputime_t delta_cpu;
+
+ if (!vtime_jiffies_changed(tsk, jiffies))
+ return;

+ delta_cpu = get_vtime_delta(tsk);
account_idle_time(delta_cpu);
}

@@ -773,6 +794,7 @@ void arch_vtime_task_switch(struct task_struct *prev)
write_seqcount_begin(&current->vtime_seqcount);
current->vtime_snap_whence = VTIME_SYS;
current->vtime_snap = sched_clock_cpu(smp_processor_id());
+ current->vtime_jiffies = jiffies;
write_seqcount_end(&current->vtime_seqcount);
}

@@ -784,6 +806,7 @@ void vtime_init_idle(struct task_struct *t, int cpu)
write_seqcount_begin(&t->vtime_seqcount);
t->vtime_snap_whence = VTIME_SYS;
t->vtime_snap = sched_clock_cpu(cpu);
+ t->vtime_jiffies = jiffies;
write_seqcount_end(&t->vtime_seqcount);
local_irq_restore(flags);
}
--
2.5.0