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

KOSAKI Motohiro
2009-05-12T10:01:38Z

>
> * tip-bot for KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote:
>
> > Commit-ID: 50fbed3bb72cbe38a665512771a91a96d028de46
> > Gitweb: http://git.kernel.org/tip/50fbed3bb72cbe38a665512771a91a96d028de46
> > Author: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
> > AuthorDate: Sat, 9 May 2009 19:14:58 +0900
> > Committer: Ingo Molnar <mingo@elte.hu>
> > CommitDate: Mon, 11 May 2009 14:32:57 +0200
> >
> > sched: cpuacct: Use bigger percpu counter batch values for stats counters
>
> -tip testing found a build failure with this patch:
>
> kernel/sched.c:9278: error: ‘percpu_counter_batch’ undeclared (first use in this function)
> kernel/sched.c:9278: error: (Each undeclared identifier is reported only once
> kernel/sched.c:9278: error: for each function it appears in.)

Oh, my fault again. Good catch!

Changelog:
since V5
- fix build error when UP

since V4
- move cpuacct_batch initialization into sched_init()

since V3
- rewirte patch description (thanks Bharata!)
- append read_mostly to cpuacct_batch
- cpuacct_batch is initialized by sched_init()

since v2
- revert using percpu_counter_sum()

since v1
- use percpu_counter_sum() instead percpu_counter_read()

---------------------------------------------------------
Subject: [PATCH v6] 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 13:28:53.000000000 +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 CONFIGCONFIG_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();