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Date: Fri, 29 May 2015 11:54:35 +0200
From: Ingo Molnar <mingo@kernel.org>
To: "Naveen N. Rao" <naveen.n.rao@linux.vnet.ibm.com>
Cc: Balbir Singh <bsingharora@gmail.com>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Peter Zijlstra <a.p.zijlstra@chello.nl>, srikar@linux.vnet.ibm.com
Subject: Re: [PATCH] proc/schedstat: Expose /proc/<pid>/schedstat if delay
 accounting is enabled
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* Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> wrote:

> On 2015/05/29 11:18AM, Ingo Molnar wrote:
> > 
> > * Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> wrote:
> > 
> > > On 2015/05/29 10:04AM, Ingo Molnar wrote:
> > > > 
> > > > * Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com> wrote:
> > > > 
> > > >  - 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).
> > 
> > Hm, indeed - I mis-read the rq-specific code - sorry.
> > 
> > So all this should really be cleaned up:
> > 
> > include/linux/sched.h:#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
> > include/linux/sched.h:#endif /* defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT) */
> > include/linux/sched.h:#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
> > kernel/sched/core.c:#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
> > kernel/sched/stats.h:#if defined(CONFIG_SCHEDSTATS) || defined(CONFIG_TASK_DELAY_ACCT)
> > kernel/sched/stats.h:#endif /* CONFIG_SCHEDSTATS || CONFIG_TASK_DELAY_ACCT */
> > 
> > by introducing an intermediate Kconfig variable, named CONFIG_SCHED_INFO or so, 
> > and selected by both SCHEDSTATS and TASK_DELAY_ACCT.
> > 
> > Please make it two patches: the first one adds CONFIG_SCHED_INFO and cleans up the 
> > code to use it, the second one uses it for the procps change.
> 
> Sure, will do.
> 
> On a related note, even though sum_exec_runtime is available unconditionally, I 
> dump all zeroes in my patch if !sched_info_on() to make it clear that some of 
> the fields are not available. Is this ok or should be display sum_exec_runtime 
> regardless of sched_info?

So I'd suggest printing -1 for non-available fields, that should be unambigous 
enough and makes it also possible to write out 0 in some cases.

That way the schedstat file should be made unconditional altogether. (And we still 
want the Kconfig cleanups as a separate patch.)

Thanks,

	Ingo