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Date:   Wed, 6 Mar 2019 13:38:34 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Yafang Shao <laoar.shao@gmail.com>
Cc:     mingo@redhat.com, LKML <linux-kernel@vger.kernel.org>,
        shaoyafang@didiglobal.com
Subject: Re: [PATCH] sched: fair: fix missed CONFIG_SCHEDSTATS
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On Wed, Mar 06, 2019 at 07:49:36PM +0800, Yafang Shao wrote:


$ grep SCHEDSTAT defconfig-build/.config
# CONFIG_SCHEDSTATS is not set
$ obbjdump -dr defconfig-build/kernel/sched/fair.o | awk '/>:$/ { F=$2 } /sched_stat/ { print F " " $0 }'
<update_curr>:                  24cd: R_X86_64_32S      __tracepoint_sched_stat_runtime+0x28
<update_curr>:                  24d9: R_X86_64_PC32     __tracepoint_sched_stat_runtime+0x24
$ patch -p1 < foo
patching file kernel/sched/fair.c
$ make O=defconfig-build kernel/sched/
make[1]: Entering directory '/usr/src/linux-2.6/defconfig-build'
Using .. as source for kernel
GEN     Makefile
CALL    ../scripts/checksyscalls.sh
CALL    ../scripts/atomic/check-atomics.sh
DESCEND  objtool
CC      kernel/sched/fair.o
AR      kernel/sched/built-in.a
make[1]: Leaving directory '/usr/src/linux-2.6/defconfig-build'
$ objdump -dr defconfig-build/kernel/sched/fair.o | awk '/>:$/ { F=$2 } /sched_stat/ { print F " " $0 }'
$ cat foo
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 8213ff6e365d..6e5ceec3b662 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -839,7 +839,8 @@ static void update_curr(struct cfs_rq *cfs_rq)
 	if (entity_is_task(curr)) {
 		struct task_struct *curtask = task_of(curr);
 
-		trace_sched_stat_runtime(curtask, delta_exec, curr->vruntime);
+		if (schedstat_enabled())
+			trace_sched_stat_runtime(curtask, delta_exec, curr->vruntime);
 		cgroup_account_cputime(curtask, delta_exec);
 		account_group_exec_runtime(curtask, delta_exec);
 	}


_1_ line, where you wanted to add _6_ ugly #ifdefs