Re: [tip:sched/core] sched: cpuacct: Use bigger percpu counter batch values for stats counters

KOSAKI Motohiro
2009-05-12T10:22:50Z

> > On Tue, 2009-05-12 at 19:01 +0900, KOSAKI Motohiro wrote:
> > > +#ifdef CONFIGCONFIG_SMP
> >
> > typo ?
>
> yes, this week is my memorial stupid one ;)

ok, assemble list indicate current patch have no typo ;)

ffffffff814ae920: 48 c7 40 30 10 eb 2a movq $0xffffffff812aeb10,0x30(%rax)
ffffffff814ae927: 81
ffffffff814ae928: c7 05 3e 37 fe ff 01 movl $0x1,-0x1c8c2(%rip) # ffffffff81492070 <scheduler_running>
ffffffff814ae92f: 00 00 00
ffffffff814ae932: 8b 05 28 52 fe ff mov -0x1add8(%rip),%eax # ffffffff81493b60 <percpu_counter_batch>
ffffffff814ae938: 89 05 36 37 fe ff mov %eax,-0x1c8ca(%rip) # ffffffff81492074 <cpuacct_batch>
ffffffff814ae93e: 41 5c pop %r12

---------------------------------------------------------
Subject: [PATCH] cpuacct: Use bigger percpu counter batch values for stats counters on archs that have VIRT_CPU_ACCOUNTING=y

percpu counters used to accumulate statistics in cpuacct controller use
the default batch value [max(2*nr_cpus, 32)] which can be too small for
archs that define VIRT_CPU_ACCOUNTING. In such archs, a tick could result in
cputime updates in the range of thousands. As a result, cpuacct_update_stats()
would end up acquiring the percpu counter spinlock on every tick which
is not good for performance.

Let those architectures to have a bigger batch threshold so that percpu counter
spinlock isn't taken on every tick. This change doesn't affect the archs which
don't define VIRT_CPU_ACCOUNTING and they continue to have the default
percpu counter batch value.

Cc: Balaji Rao <balajirrao@gmail.com>
Cc: Dhaval Giani <dhaval@linux.vnet.ibm.com>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Bharata B Rao <bharata@linux.vnet.ibm.com>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
---
kernel/sched.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)

Index: b/kernel/sched.c
===================================================================
--- a/kernel/sched.c 2009-05-12 13:12:59.000000000 +0900
+++ b/kernel/sched.c 2009-05-12 19:04:49.000000000 +0900
@@ -870,6 +870,8 @@ static __read_mostly int scheduler_runni
*/
int sysctl_sched_rt_runtime = 950000;

+static __read_mostly s32 cpuacct_batch;
+
static inline u64 global_rt_period(void)
{
return (u64)sysctl_sched_rt_period * NSEC_PER_USEC;
@@ -9284,6 +9286,10 @@ void __init sched_init(void)

perf_counter_init();

+#ifdef CONFIG_SMP
+ cpuacct_batch = jiffies_to_cputime(percpu_counter_batch);
+#endif
+
scheduler_running = 1;
}

@@ -10457,7 +10463,8 @@ static void cpuacct_update_stats(struct
ca = task_ca(tsk);

do {
- percpu_counter_add(&ca->cpustat[idx], val);
+ __percpu_counter_add(&ca->cpustat[idx], val, cpuacct_batch);
+
ca = ca->parent;
} while (ca);
rcu_read_unlock();