Messages in this thread Patch in this message | | | From | KOSAKI Motohiro <> | Subject | Re: [PATCH v3] cpuacct: VIRT_CPU_ACCOUNTING don't prevent percpu cputime count | Date | Sat, 9 May 2009 18:26:08 +0900 (JST) |
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> > * KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> wrote: > > > > > Changelog: > > since v2 > > - revert using percpu_counter_sum() > > > > since v1 > > - use percpu_counter_sum() instead percpu_counter_read() > > > > > > ------------------------------------- > > Subject: [PATCH v3] 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 | 6 +++++- > > 1 file changed, 5 insertions(+), 1 deletion(-) > > > > Index: b/kernel/sched.c > > =================================================================== > > --- a/kernel/sched.c 2009-04-30 11:37:47.000000000 +0900 > > +++ b/kernel/sched.c 2009-05-07 16:34:00.000000000 +0900 > > @@ -10221,6 +10221,7 @@ struct cpuacct { > > }; > > > > struct cgroup_subsys cpuacct_subsys; > > +static s32 cpuacct_batch; > > should be __read_mostly i guess. > > > > > /* 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); > > So this is a once per boot condition? Why not initialize it in > sched_init() or so? (instead of incuring this ugly check all the > time)
Thanks! fixed.
Changelog: 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 v4] 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 | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
Index: b/kernel/sched.c =================================================================== --- a/kernel/sched.c 2009-05-09 16:48:08.000000000 +0900 +++ b/kernel/sched.c 2009-05-09 18:16:00.000000000 +0900 @@ -824,8 +824,12 @@ static struct file_operations sched_feat .release = single_release, }; +static __read_mostly s32 cpuacct_batch; + static __init int sched_init_debug(void) { + cpuacct_batch = jiffies_to_cputime(percpu_counter_batch); + debugfs_create_file("sched_features", 0644, NULL, NULL, &sched_feat_fops); @@ -10457,7 +10461,8 @@ 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();
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