linux-kernel - [PATCH] sched/fair: Clean up comment in nohz_idle

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <20181127110110.5533-1-andrea.parri@amarulasolutions.com>
Date:   Tue, 27 Nov 2018 12:01:10 +0100
From:   Andrea Parri <andrea.parri@...rulasolutions.com>
To:     linux-kernel@...r.kernel.org
Cc:     Andrea Parri <andrea.parri@...rulasolutions.com>,
        Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: [PATCH] sched/fair: Clean up comment in nohz_idle_balance()

Concerning the comment associated to the atomic_fetch_andnot() in
nohz_idle_balance(), Vincent explains [1]:

  "[...] the comment is useless and can be removed [...]  it was
   referring to a line code above the comment that was present in
   a previous iteration of the patchset. This line disappeared in
   final version but the comment has stayed."

So remove the comment.

Vincent also points out that the full ordering associated to the
atomic_fetch_andnot() primitive could be relaxed, but this patch
insists on the current more conservative/fully ordered solution:

"Performance" isn't a concern, stay away from "correctness"/subtle
relaxed (re)ordering if possible..., just make sure not to confuse
the next reader with misleading/out-of-date comments.

[1] http://lkml.kernel.org/r/CAKfTPtBjA-oCBRkO6__npQwL3+HLjzk7riCcPU1R7YdO-EpuZg@mail.gmail.com

Suggested-by: Vincent Guittot <vincent.guittot@...aro.org>
Signed-off-by: Andrea Parri <andrea.parri@...rulasolutions.com>
Cc: Ingo Molnar <mingo@...hat.com>
Cc: Peter Zijlstra <peterz@...radead.org>
Cc: Vincent Guittot <vincent.guittot@...aro.org>
---
 kernel/sched/fair.c | 4 +---
 1 file changed, 1 insertion(+), 3 deletions(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index ac855b2f47746..db514993565b2 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -9533,9 +9533,7 @@ static bool nohz_idle_balance(struct rq *this_rq, enum cpu_idle_type idle)
 		return false;
 	}
 
-	/*
-	 * barrier, pairs with nohz_balance_enter_idle(), ensures ...
-	 */
+	/* could be _relaxed() */
 	flags = atomic_fetch_andnot(NOHZ_KICK_MASK, nohz_flags(this_cpu));
 	if (!(flags & NOHZ_KICK_MASK))
 		return false;
-- 
2.17.1