linux-kernel - [PATCH] sched/fair: refine maximum periods for decay

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: <1470378840-15206-1-git-send-email-leo.yan@linaro.org>
Date:	Fri,  5 Aug 2016 14:34:00 +0800
From:	Leo Yan <leo.yan@...aro.org>
To:	Ingo Molnar <mingo@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org
Cc:	Leo Yan <leo.yan@...aro.org>
Subject: [PATCH] sched/fair: refine maximum periods for decay_load

In current code, decay_load() will consider to set load value to zero
after passing 32*64 ms. So this means max_load * (0.5^64) ~= 0.

Kernel can support maximum number of processes and threads to 2^29 and
set task with highest priority with nice=-20 (weight = 88761). So in
worst case, one CPU may have maximum load value is:

    max_load = 2^29 * 88761 < 2^46

In theory after pass 46 periods we can ensure load value will be decayed
to zero. So this patch is to change maximum periods from 64 to 48.

Signed-off-by: Leo Yan <leo.yan@...aro.org>
---
 kernel/sched/fair.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index e342159..55cb134 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2622,7 +2622,7 @@ static __always_inline u64 decay_load(u64 val, u64 n)

 	if (!n)
 		return val;
-	else if (unlikely(n > LOAD_AVG_PERIOD * 63))
+	else if (unlikely(n > LOAD_AVG_PERIOD * 47))
 		return 0;

 	/* after bounds checking we can collapse to 32-bit */
-- 
1.9.1