linux-kernel - Hack bench regression with CONFIG_SLUB_CPU

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Message-ID: <51F0DB11.2080508@linux.vnet.ibm.com>
Date:	Thu, 25 Jul 2013 13:30:17 +0530
From:	Raghavendra K T <raghavendra.kt@...ux.vnet.ibm.com>
To:	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
CC:	"David S. Miller" <davem@...emloft.net>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Gao feng <gaofeng@...fujitsu.com>
Subject: Hack bench regression with CONFIG_SLUB_CPU_PARTIAL disabled (info
 only)

Hi,

While testing hackbench with 3.11-rc1 I observed hackbench testcase
took too long to complete (32 vcpu kvm guest on 32 core HT off machine).

hackbench 1x degraded by 3 time (40sec vs 112sec)
hackbench 2x degraded by around 20time (90sec vs 1800 sec)

When I bisected, I found that I had CONFIG_SLUB_CPU_PARTIAL
accidentally disabled.
I understand that  CONFIG_SLUB_CPU_PARTIAL=y by default and the config
option is to provide determinism for RT kernels and thus it is not a
problem.
But thought of sharing this here so that if somebody runs into same 
issue accidently, it would save their time.

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