linux-kernel - Re: [PATCH] sched: fair: fix missed CONFIG

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Date:   Wed, 6 Mar 2019 12:27:07 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Yafang Shao <laoar.shao@...il.com>
Cc:     mingo@...hat.com, LKML <linux-kernel@...r.kernel.org>,
        shaoyafang@...iglobal.com
Subject: Re: [PATCH] sched: fair: fix missed CONFIG_SCHEDSTATS

On Wed, Mar 06, 2019 at 06:15:39PM +0800, Yafang Shao wrote:
> On Wed, Mar 6, 2019 at 6:09 PM Peter Zijlstra <peterz@...radead.org> wrote:
> >
> > On Wed, Mar 06, 2019 at 04:43:46PM +0800, Yafang Shao wrote:
> > > When I'm using trace_sched_stat_{iowait, blocked, wait, sleep} to
> > > measure how long the processes are stalled, there's always no output from
> > > trace_pipe while there're really some tasks in uninterruptible sleep
> > > state. That makes me confused, so I try to investigate why.
> > > Finally I find the reason is that CONFIG_SCHEDSTATS is not set.
> > >
> > > To avoid such kind of confusion, we should not expose these tracepoints
> > > if CONFIG_SCHEDSTATS is not set.
> >
> > Yeah, lets not sprinkle #ifdef. Big fat NAK.
> >
> > Also, the below seem to indicate your compiler is stupid. Without
> > CONFIG_SCHEDSTAT, schedstat_enabled() should be a constant 0 and DCE
> > should delete all code.
> >
> 
> My compiler is GCC-7.3.0.
> I don't know which comipler could be smart enough to remove the
> definition of these tracepoints.
> Could you pls. tell me what compiler you are using ?

Just look at the generated code...