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

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Message-ID: <20150625182707.GA15883@naverao1-tp.in.ibm.com>
Date:	Thu, 25 Jun 2015 23:57:07 +0530
From:	"Naveen N. Rao" <naveen.n.rao@...ux.vnet.ibm.com>
To:	Cong Wang <xiyou.wangcong@...il.com>
Cc:	Balbir Singh <bsingharora@...il.com>,
	Ingo Molnar <mingo@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] proc/schedstat: Expose /proc/<pid>/schedstat if delay
 accounting is enabled

On 2015/06/25 11:00AM, Cong Wang wrote:
> On Thu, May 28, 2015 at 2:11 AM, Balbir Singh <bsingharora@...il.com> wrote:
> > On Mon, May 25, 2015 at 12:42 PM, 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.
> >>
> 
> [...]
> 
> > The change looks reasonable, from what I can understand you want these
> > changes so that you can use /proc/<pid>/schedstat instead of the
> > netlink interface when CONFIG_TASK_DELAY_ACCT is enabled.
> >
> 
> Why?
> 
> If you need the procfs interface, just enable CONFIG_SCHEDSTATS.
> If you need the netlink interface, enable CONFIG_TASK_DELAY_ACCT.
> They are just two different interfaces for getting the same sched
> information, so why make this change?
> 
> There must be some reason you don't want to enable
> CONFIG_SCHEDSTATS? If so, please add it in the changelog.
> 
> My guess is it depends on DEBUG_KERNEL which is not what you
> want? But I see no reason it should have that dependency, it just
> exposes some stats, looks like can be just removed (and moved out
> of Kconfig,debug of course).

The primary issue with CONFIG_SCHEDSTATS is the (slight) additional 
overhead it introduces, per Kconfig. Due to this, it is not enabled by 
default by some of the distro kernels.

Regards,
Naveen

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