linux-kernel - Re: [PATCH 1/4] x86_64: (SPARSE_VIRTUAL doubles sparsemem speed)

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Date:	Sun, 8 Apr 2007 00:18:44 +0200
From:	Andi Kleen <ak@...e.de>
To:	Christoph Lameter <clameter@....com>
Cc:	Andy Whitcroft <apw@...dowen.org>,
	Martin Bligh <mbligh@...gle.com>,
	Dave Hansen <hansendc@...ibm.com>,
	linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
	linux-mm@...ck.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH 1/4] x86_64: (SPARSE_VIRTUAL doubles sparsemem speed)

On Sunday 08 April 2007 00:06:13 Christoph Lameter wrote:

> Results:
> 
> x86_64 boot with virtual memmap
> 
> Format:               #events totaltime (min/avg/max)
> 
> kfree_virt_to_page       598430 5.6ms(3ns/9ns/322ns)
> 
> x86_64 boot regular sparsemem
> 
> kfree_virt_to_page       596360 10.5ms(4ns/18ns/28.7us)
> 
> 
> On average sparsemem virtual takes half the time than of sparsemem.

Nice.  But on what workloads? 

Anyways it looks promising. I hope we can just
replace old style sparsemem support with this for x86-64.

> Time is measured using the cycle counter (TSC on IA32, ITC on IA64) which has
> a very low latency.

Sorry that triggered my usual RDTSC rant...

Not on NetBurst (hundred of cycles) And on the others (C2,K8) it is a bit dangerous 
to measure short code blocks because RDTSC is not guaranteed ordered with the surrounding 
instructions.

-Andi
 
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