linux-kernel - Re: [rfc 00/45] [RFC] CPU ops and a rework of per cpu data handling on x86

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Message-ID: <Pine.LNX.4.64.0711191932290.21689@schroedinger.engr.sgi.com>
Date:	Mon, 19 Nov 2007 19:33:25 -0800 (PST)
From:	Christoph Lameter <clameter@....com>
To:	Andi Kleen <ak@...e.de>
cc:	David Miller <davem@...emloft.net>, akpm@...ux-foundation.org,
	travis@....com, mathieu.desnoyers@...ymtl.ca,
	linux-kernel@...r.kernel.org
Subject: Re: [rfc 00/45] [RFC] CPU ops and a rework of per cpu data handling
 on x86_64

n Tue, 20 Nov 2007, Andi Kleen wrote:

> 
> > Although we have a per-cpu area base in a fixed global register
> > for addressing, the above isn't beneficial on sparc64 because
> > the atomic is much slower than doing a:
> >
> > 	local_irq_disable();
> > 	nonatomic_percpu_memory_op();
> > 	local_irq_enable();
> 
> Again might be pointing out the obvious, but you 
> need of course save_flags()/restore_flags(), not disable/enable().
> 
> If it was just disable/enable x86 could do it much faster too 
> and Christoph probably would never felt the need to approach
> this project for his SLUB fast path.

I already have no need for that anymore with the material now in Andrews 
tree. However, this cuts out another 6 cycles from the fastpath and I 
found that the same principles reduce overhead all over the kernel.


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