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From: "Siddha, Suresh B" <suresh.b.siddha@intel.com>
To: Ken Chen <kenchen@google.com>
Cc: Ingo Molnar <mingo@elte.hu>,
	Nick Piggin <nickpiggin@yahoo.com.au>,
	"Siddha, Suresh B" <suresh.b.siddha@intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [patch] sched: fix improper load balance across sched domain
Date: Tue, 16 Oct 2007 19:23:03 -0700	[thread overview]
Message-ID: <20071017022303.GA27457@linux-os.sc.intel.com> (raw)
In-Reply-To: <b040c32a0710161207s4d6d4d4cq1fa7f0dd1a7f017d@mail.gmail.com>

On Tue, Oct 16, 2007 at 12:07:06PM -0700, Ken Chen wrote:
> We recently discovered a nasty performance bug in the kernel CPU load
> balancer where we were hit by 50% performance regression.
> 
> When tasks are assigned to a subset of CPUs that span across
> sched_domains (either ccNUMA node or the new multi-core domain) via
> cpu affinity, kernel fails to perform proper load balance at
> these domains, due to several logic in find_busiest_group() miss
> identified busiest sched group within a given domain. This leads to
> inadequate load balance and causes 50% performance hit.
> 
> To give you a concrete example, on a dual-core, 2 socket numa system,
> there are 4 logical cpu, organized as:

oops, this issue can easily happen when cores are not sharing caches. I
think this is what happening on your setup, right?

thanks,
suresh

  reply	other threads:[~2007-10-17  2:23 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-10-16 19:07 [patch] sched: fix improper load balance across sched domain Ken Chen
2007-10-17  2:23 ` Siddha, Suresh B [this message]
2007-10-17 17:08   ` Ken Chen
2007-10-17  7:20 ` Ingo Molnar

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