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    SubjectRe: [PATCH v3] cpuacct: VIRT_CPU_ACCOUNTING don't prevent percpu cputime count

    * 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)

    Ingo


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