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From:   Yafang Shao <laoar.shao@gmail.com>
Date:   Wed, 6 Mar 2019 19:49:36 +0800
Message-ID: <CALOAHbB7EZ83R3gHcGa9oZWq=7CEgBkL2cXav_7N13u4U44+uA@mail.gmail.com>
Subject: Re: [PATCH] sched: fair: fix missed CONFIG_SCHEDSTATS
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     mingo@redhat.com, LKML <linux-kernel@vger.kernel.org>,
        shaoyafang@didiglobal.com
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On Wed, Mar 6, 2019 at 7:27 PM Peter Zijlstra <peterz@infradead.org> wrote:
>
> 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@infradead.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...

When CONFIG_SCHEDSTATS  is not set,
I have objdumped the vmlinux, and the perf_trace_sched_stat_template
is still there withou my patch.

$ objdump -D vmlinux > vmlinux.asm
$ cat vmlinux.asm | grep trace_sched_stat
ffffffff810b3b40 <perf_trace_sched_stat_template>:
...

So I can't get your point really.
Forgive me if I missed something.

Thanks
Yafang