linux-kernel - Re: [PATCH] Fix longstanding load balancing bug in the scheduler.

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Date:	Sat, 9 Sep 2006 12:56:16 -0700 (PDT)
From:	Christoph Lameter <clameter@....com>
To:	"Siddha, Suresh B" <suresh.b.siddha@...el.com>
cc:	akpm@...l.org, linux-kernel@...r.kernel.org, npiggin@...e.de,
	mingo@...e.hu
Subject: Re: [PATCH] Fix longstanding load balancing bug in the scheduler.

On Fri, 8 Sep 2006, Christoph Lameter wrote:

> > one or more, it is unnecessary for the common case.
> 
> The common case is an arch with much less cpus. The maxinum on i386
> f.e. is 255 meaning 8 bytes. That fits in the cacheline that is already
> used for the stack frame of the calling function. 

Ughh. Wrong. 255 cpus require 32 bytes. System rarely have that 
much. If you configure a kernel with less than 32 cpus then this will be 
one word on the stack.

Also note that the patch restricts the search to online cpus. The 
scheduler will check offline cpus without this patch. That may actually 
result in speed improvements since the cachelines from offline cpus are
no longer brought in during the search for the busiest group / cpu.

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