linux-kernel - [PATCH 2/2] kernel/latencytop.c: remove unnecessary checks for latencytop

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Date:   Tue, 26 Feb 2019 19:46:02 +0800
From:   Lin Feng <linf@...gsu.com>
To:     linux-kernel@...r.kernel.org
Cc:     akpm@...ux-foundation.org, adobriyan@...il.com, fabf@...net.be,
        arjan@...radead.org, linf@...gsu.com
Subject: [PATCH 2/2] kernel/latencytop.c: remove unnecessary checks for latencytop_enabled

1. In latencytop source codes, we only have such calling chain:
account_scheduler_latency(struct task_struct *task, int usecs, int inter)
{
        if (unlikely(latencytop_enabled)) /* the outtermost check */
                __account_scheduler_latency(task, usecs, inter);
}
__account_scheduler_latency
    account_global_scheduler_latency
        if (!latencytop_enabled)

So, the inner check for latencytop_enabled is not necessary at all.

2. In clear_all_latency_tracing and now is called
clear_tsk_latency_tracing the check for latencytop_enabled is redundant
and buggy to some extent.
We have no reason to refuse clearing the /proc/$pid/latency if
latencytop_enabled is set to 0, considering that if we use latencytop
manually by echo 0 > /proc/sys/kernel/latencytop, then we want to clear
/proc/$pid/latency and failed.
Aslo we don't have such check in brother function
clear_global_latency_tracing.

Notes: These changes only visible to users who sets CONFIG_LATENCYTOP and
won't change user tool latencytop's behaviors.

Signed-off-by: Lin Feng <linf@...gsu.com>
---
 kernel/latencytop.c | 6 ------
 1 file changed, 6 deletions(-)

diff --git a/kernel/latencytop.c b/kernel/latencytop.c
index 9e794b49791e..897895efafd9 100644
--- a/kernel/latencytop.c
+++ b/kernel/latencytop.c
@@ -71,9 +71,6 @@ void clear_tsk_latency_tracing(struct task_struct *p)
 {
 	unsigned long flags;

-	if (!latencytop_enabled)
-		return;
-
 	raw_spin_lock_irqsave(&latency_lock, flags);
 	memset(&p->latency_record, 0, sizeof(p->latency_record));
 	p->latency_record_count = 0;
@@ -96,9 +93,6 @@ account_global_scheduler_latency(struct task_struct *tsk,
 	int firstnonnull = MAXLR + 1;
 	int i;

-	if (!latencytop_enabled)
-		return;
-
 	/* skip kernel threads for now */
 	if (!tsk->mm)
 		return;
-- 
2.20.1