linux-kernel - Re: [PATCH] proc/schedstat: Expose /proc/<pid>/schedstat if delay accounting is enabled

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Date:	Fri, 29 May 2015 14:25:04 +0530
From:	"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Balbir Singh <bsingharora@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	srikar@...ux.vnet.ibm.com
Subject: Re: [PATCH] proc/schedstat: Expose /proc/<pid>/schedstat if delay
 accounting is enabled

On 2015/05/29 10:04AM, Ingo Molnar wrote:
> 
> * Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com> wrote:
> 
> > /proc/<pid>/schedstat is currently only available if CONFIG_SCHEDSTATS is
> > enabled. But, all the fields that this exposes are available and valid
> > if CONFIG_TASK_DELAY_ACCT is enabled as well.
> > 
> > Signed-off-by: Naveen N. Rao <naveen.n.rao@...ux.vnet.ibm.com>
> > ---
> >  fs/proc/base.c | 11 +++++++----
> >  1 file changed, 7 insertions(+), 4 deletions(-)
> > 
> > diff --git a/fs/proc/base.c b/fs/proc/base.c
> > index 093ca14..3ece303 100644
> > --- a/fs/proc/base.c
> > +++ b/fs/proc/base.c
> > @@ -304,14 +304,17 @@ static int proc_pid_stack(struct seq_file *m, struct pid_namespace *ns,
> >  }
> >  #endif
> >  
> > +#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
> > +#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
> > +#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
> 

Hi Ingo,
Thanks for the review.

> So such #ifdef parades are ugly and are usually a sign of some problem with the 
> patch - as in this case.
> 
> But there's deeper problems as well:
> 
> /*
>  * Provides /proc/PID/schedstat
>  */
> static int proc_pid_schedstat(struct seq_file *m, struct pid_namespace *ns,
>                               struct pid *pid, struct task_struct *task)
> {
>         seq_printf(m, "%llu %llu %lu\n",
>                    (unsigned long long)task->se.sum_exec_runtime,
>                    (unsigned long long)task->sched_info.run_delay,
>                    task->sched_info.pcount);
> 
>         return 0;
> }
> 
>  - The sum_exec_runtime field is available unconditionally.
> 
>  - But the sched_info.run_delay field is only maintained if CONFIG_SCHEDSTATS is
>    enabled.
> 
>  - Also, the sched_info.pcount field is again only maintained if CONFIG_SCHEDSTATS 
>    is enabled.

I may be missing something, but from my reading of the code, the above 
are maintained if any one of CONFIG_SCHEDSTATS or CONFIG_TASK_DELAY_ACCT 
are enabled (from kernel/sched/stats.h).

Only the runqueue-specific sched_info is tracked with CONFIG_SCHEDSTATS 
separately [kernel/sched/stats.c and the corresponding global 
/proc/schedstat]


Regards,
Naveen

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