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    SubjectRe: [tip:sched/core] sched: cpuacct: Use bigger percpu counter batch values for stats counters
    Date
    > 
    > * Balbir Singh <balbir@linux.vnet.ibm.com> wrote:
    >
    > > * KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com> [2009-05-12 19:13:42]:
    > >
    > > > > > +#ifdef CONFIGCONFIG_SMP
    > > > > > + cpuacct_batch = jiffies_to_cputime(percpu_counter_batch);
    > > > > > +#endif
    > > > >
    > > > > Slow down and compile patches before sending them out.. please. That
    > > > > is a basic expectation if you expect it to be merged.
    > > >
    > > > Unfortunately, this mistake pass test successfully ;)
    > > > it because cpuacct_batch=0 works even SMP.
    > > >
    > >
    > > OK, BTW, using an #ifdef right in the middle of a function makes
    > > the code harder to read, can't we use an inline function to
    > > abstract out SMP?
    >
    > or rather, to make cpuacct_batch have a sane value on UP too. (1?
    > 0?)

    umm..

    I've reviewed my patch again.
    but sched_init() already has multiple #ifdef SMP. Thus I don't think
    cosmetic changing improve readability largely.



    ------------------------------------
    Subject: [PATCH] sched: cpuacct: Use bigger percpu counter batch values for stats counters

    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.

    v7:
    - fix typo and changelog

    v6:
    - fix build error when UP

    v5:
    - move cpuacct_batch initialization into sched_init()

    v4:
    - rewrite patch description (thanks Bharata!)
    - append read_mostly to cpuacct_batch
    - cpuacct_batch is initialized by sched_init_debug()

    v3:
    - revert using percpu_counter_sum()

    v2:
    - use percpu_counter_sum() instead percpu_counter_read()

    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();



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