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Re: [PATCH v2 4/6] x86: Add clear_page_nocache

To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCH v2 4/6] x86: Add clear_page_nocache
From: Andi Kleen <ak@linux.intel.com>
Date: Mon, 13 Aug 2012 09:27:53 -0700
Cc: Jan Beulich <JBeulich@suse.com>, Andy Lutomirski <luto@amacapital.net>, Robert Richter <robert.richter@amd.com>, Johannes Weiner <hannes@cmpxchg.org>, Hugh Dickins <hughd@google.com>, Alex Shi <alex.shu@intel.com>, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>, x86@kernel.org, linux-mm@kvack.org, Thomas Gleixner <tglx@linutronix.de>, Andrew Morton <akpm@linux-foundation.org>, linux-mips@linux-mips.org, Tim Chen <tim.c.chen@linux.intel.com>, linuxppc-dev@lists.ozlabs.org, Andrea Arcangeli <aarcange@redhat.com>, Ingo Molnar <mingo@redhat.com>, Mel Gorman <mgorman@suse.de>, linux-kernel@vger.kernel.org, linux-sh@vger.kernel.org, sparclinux@vger.kernel.org, "H. Peter Anvin" <hpa@zytor.com>
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> Moving 64 bytes per cycle is faster on Sandy Bridge, but slower on
> Westmere. Any preference? ;)

You have to be careful with these benchmarks.

- You need to make sure the data is cache cold, cache hot is misleading.
- The numbers can change if you have multiple CPUs doing this in parallel.

-Andi

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