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    SubjectRe: [PATCH] sched: fair: fix missed CONFIG_SCHEDSTATS
    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 ?

    > > @@ -976,6 +982,7 @@ static void update_curr_fair(struct rq *rq)
    > > static inline void
    > > update_stats_enqueue(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
    > > {
    > > +#ifdef CONFIG_SCHEDSTATS
    > > if (!schedstat_enabled())
    > > return;
    > >
    > > @@ -988,12 +995,13 @@ static void update_curr_fair(struct rq *rq)
    > >
    > > if (flags & ENQUEUE_WAKEUP)
    > > update_stats_enqueue_sleeper(cfs_rq, se);
    > > +#endif
    > > }
    > >
    > > static inline void
    > > update_stats_dequeue(struct cfs_rq *cfs_rq, struct sched_entity *se, int flags)
    > > {
    > > -
    > > +#ifdef CONFIG_SCHEDSTATS
    > > if (!schedstat_enabled())
    > > return;
    > >
    > > @@ -1014,6 +1022,7 @@ static void update_curr_fair(struct rq *rq)
    > > __schedstat_set(se->statistics.block_start,
    > > rq_clock(rq_of(cfs_rq)));
    > > }
    > > +#endif
    > > }
    > >
    > > /*
    > > @@ -4090,6 +4099,7 @@ static void clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se)
    > > update_stats_curr_start(cfs_rq, se);
    > > cfs_rq->curr = se;
    > >
    > > +#ifdef CONFIG_SCHEDSTATS
    > > /*
    > > * Track our maximum slice length, if the CPU's load is at
    > > * least twice that of our own weight (i.e. dont track it
    > > @@ -4100,6 +4110,7 @@ static void clear_buddies(struct cfs_rq *cfs_rq, struct sched_entity *se)
    > > max((u64)schedstat_val(se->statistics.slice_max),
    > > se->sum_exec_runtime - se->prev_sum_exec_runtime));
    > > }
    > > +#endif
    > >
    > > se->prev_sum_exec_runtime = se->sum_exec_runtime;
    > > }
    > > --
    > > 1.8.3.1
    > >

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