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Subject[PATCH v2] cpuacct: VIRT_CPU_ACCOUNTING don't prevent percpu cputime count
Date

Changelog:
since v1
- use percpu_counter_sum() instead percpu_counter_read()


-------------------------------------
Subject: [PATCH v2] cpuacct: VIRT_CPU_ACCOUNTING don't prevent percpu cputime count
cpuacct_update_stats() is called at every tick updating. and it use percpu_counter
for avoiding performance degression.

For archs which define VIRT_CPU_ACCOUNTING, every tick would result
in >1000 units of cputime updates and since this is much much greater
than percpu_batch_counter, we end up taking spinlock on every tick.

This patch change batch rule. now, any cpu can store "percpu_counter_bach * jiffies"
cputime in per-cpu cache.
it mean this patch don't have behavior change if VIRT_CPU_ACCOUNTING=n.

Cc: Bharata B Rao <bharata@linux.vnet.ibm.com>
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: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
---
kernel/sched.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
Index: b/kernel/sched.c
===================================================================
--- a/kernel/sched.c 2009-04-30 11:37:47.000000000 +0900
+++ b/kernel/sched.c 2009-04-30 14:17:00.000000000 +0900
@@ -10221,6 +10221,7 @@ struct cpuacct {
};

struct cgroup_subsys cpuacct_subsys;
+static s32 cpuacct_batch;

/* return cpu accounting group corresponding to this container */
static inline struct cpuacct *cgroup_ca(struct cgroup *cgrp)
@@ -10250,6 +10251,9 @@ static struct cgroup_subsys_state *cpuac
if (!ca->cpuusage)
goto out_free_ca;

+ if (!cpuacct_batch)
+ cpuacct_batch = jiffies_to_cputime(percpu_counter_batch);
+
for (i = 0; i < CPUACCT_STAT_NSTATS; i++)
if (percpu_counter_init(&ca->cpustat[i], 0))
goto out_free_counters;
@@ -10376,7 +10380,7 @@ static int cpuacct_stats_show(struct cgr
int i;

for (i = 0; i < CPUACCT_STAT_NSTATS; i++) {
- s64 val = percpu_counter_read(&ca->cpustat[i]);
+ s64 val = percpu_counter_sum(&ca->cpustat[i]);
val = cputime64_to_clock_t(val);
cb->fill(cb, cpuacct_stat_desc[i], val);
}
@@ -10446,7 +10450,7 @@ 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();



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