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    SubjectRe: [PATCH v3] cpuacct: VIRT_CPU_ACCOUNTING don't prevent percpu cputime count
    Date
    > > On Sat, 2009-05-09 at 18:26 +0900, KOSAKI Motohiro wrote:
    > > >
    > > > 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);
    > >
    > > I'm pretty user you can select cpu accounting without SCHED_DEBUG...
    >
    > Grr, yes, it's idiot ;)
    > I'll fix it soon.


    Done.


    Changelog:
    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_debug()

    since v2
    - revert using percpu_counter_sum()

    since v1
    - use percpu_counter_sum() instead percpu_counter_read()


    ---------------------------------------------------------
    Subject: [PATCH v5] 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 18:57:35.000000000 +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 +9286,8 @@ void __init sched_init(void)

    perf_counter_init();

    + cpuacct_batch = jiffies_to_cputime(percpu_counter_batch);
    +
    scheduler_running = 1;
    }

    @@ -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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