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Date: Tue, 2 Jun 2015 09:58:25 +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 11:54AM, Ingo Molnar wrote:
> > 
> > > > 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.
> 
> Per Documentation/scheduler/sched-stats.txt (and the linked latency.c there), 
> user-space seems to be expecting unsigned values here. Would displaying -1 here 
> be ok?

Probably not (the code is silly, why doesn't it split up the string and use 
atol()?) - hopefully real user-space is better? Can you try some real, packaged up 
tools that read schedstats, to see whether they work with -1?

Thanks,

	Ingo