linux-kernel - Re: [patch 2/2] sched: allow cpuacct stats to be reset

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Message-ID: <6599ad830802282148g7f309995l450fc15074234cd7@mail.gmail.com>
Date:	Thu, 28 Feb 2008 21:48:51 -0800
From:	"Paul Menage" <menage@...gle.com>
To:	"Dhaval Giani" <dhaval@...ux.vnet.ibm.com>
Cc:	vatsa@...ux.vnet.ibm.com, balbir@...ux.vnet.ibm.com, mingo@...e.hu,
	linux-kernel@...r.kernel.org, a.p.zijlstra@...llo.nl,
	akpm@...ux-foundation.org, skumar@...ux.vnet.ibm.com
Subject: Re: [patch 2/2] sched: allow cpuacct stats to be reset

On Thu, Feb 28, 2008 at 8:32 PM, Dhaval Giani <dhaval@...ux.vnet.ibm.com> wrote:
> Currently the schedstats implementation does not allow the statistics
>  to be reset. This patch aims to allow that.
>
>  echo 0 > cpuacct.usage
>
>  resets the usage. Any other value is not allowed and returns -EINVAL.
>
>  Signed-off-by: Dhaval Giani <dhaval@...ux.vnet.ibm.com>
>
>  ---
>   kernel/sched.c |   24 ++++++++++++++++++++++++
>   1 files changed, 24 insertions(+)
>
>  Index: linux-2.6/kernel/sched.c
>  ===================================================================
>  --- linux-2.6.orig/kernel/sched.c       2008-02-28 20:05:27.000000000 +0530
>  +++ linux-2.6/kernel/sched.c    2008-02-28 20:05:30.000000000 +0530
>  @@ -8243,10 +8243,34 @@ static u64 cpuusage_read(struct cgroup *
>         return totalcpuusage;
>   }
>
>  +static int cpuusage_write(struct cgroup *cgrp, struct cftype *cftype,
>  +                                                               u64 reset)
>  +{
>  +       struct cpuacct *ca = cgroup_ca(cgrp);
>  +       int err = 0;
>  +       int i;
>  +
>  +       if (reset) {
>  +               err = -EINVAL;
>  +               goto out;
>  +       }
>  +
>  +       for_each_possible_cpu(i) {
>  +               u64 *cpuusage = percpu_ptr(ca->cpuusage, i);
>  +
>  +               spin_lock_irq(&cpu_rq(i)->lock);
>  +               *cpuusage = 0;
>  +               spin_unlock_irq(&cpu_rq(i)->lock);
>  +       }
>  +out:
>  +       return err;
>  +}
>  +
>   static struct cftype files[] = {
>         {
>                 .name = "usage",
>                 .read_uint = cpuusage_read,
>  +               .write_uint = cpuusage_write,
>         },
>   };
>

Can I suggest, in order to be more generic, that this patch instead
set each CPU's counter to the written value divided by the number of
CPUs? (Either forgetting the remainder, or spreading it among the
first few CPUs).

Paul
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