From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail190.messagelabs.com (mail190.messagelabs.com [216.82.249.51]) by kanga.kvack.org (Postfix) with SMTP id 937F56B01F0 for ; Tue, 6 Apr 2010 07:57:42 -0400 (EDT) Message-ID: <4BBB2134.9090301@redhat.com> Date: Tue, 06 Apr 2010 14:55:32 +0300 From: Avi Kivity MIME-Version: 1.0 Subject: Re: [PATCH 00 of 41] Transparent Hugepage Support #17 References: <20100405120906.0abe8e58.akpm@linux-foundation.org> <20100405193616.GA5125@elte.hu> <20100405232115.GM5825@random.random> <20100406011345.GT5825@random.random> <4BBB052D.8040307@redhat.com> In-Reply-To: <4BBB052D.8040307@redhat.com> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: owner-linux-mm@kvack.org To: Linus Torvalds Cc: Andrea Arcangeli , Pekka Enberg , Ingo Molnar , Andrew Morton , linux-mm@kvack.org, Marcelo Tosatti , Adam Litke , Izik Eidus , Hugh Dickins , Nick Piggin , Rik van Riel , Mel Gorman , Dave Hansen , Benjamin Herrenschmidt , Mike Travis , KAMEZAWA Hiroyuki , Christoph Lameter , Chris Wright , bpicco@redhat.com, KOSAKI Motohiro , Balbir Singh , Arnd Bergmann , "Michael S. Tsirkin" , Peter Zijlstra , Johannes Weiner , Daisuke Nishimura List-ID: On 04/06/2010 12:55 PM, Avi Kivity wrote: > > Here is a microbenchmark demonstrating the hit (non-virtualized); it > simulates a pointer-chasing application with a varying working set. > It is easy to see when the working set overflows the various caches, > and later when the page tables overflow the caches. For > virtualization the hit will be a factor of 3 instead of 2, and will > come earlier since the page tables are bigger. > And here is the same thing with guest latencies as well: Random memory read latency, in nanoseconds, according to working set and page size. ------- host ------ ------------- guest ----------- --- hpage=4k --- -- hpage=2M - size 4k 2M 4k/4k 2M/4k 4k/2M 2M/2M 4k 4.9 4.9 5.0 4.9 4.9 4.9 16k 4.9 4.9 5.0 4.9 5.0 4.9 64k 7.6 7.6 7.9 7.8 7.8 7.8 256k 15.1 8.1 15.9 10.3 15.4 9.0 1M 28.5 23.9 29.3 37.9 29.3 24.6 4M 31.8 25.3 37.5 42.6 35.5 26.0 16M 94.8 79.0 110.7 107.3 92.0 77.3 64M 260.9 224.2 294.2 247.8 251.5 207.2 256M 269.8 248.8 313.9 253.1 260.1 230.3 1G 278.1 246.3 331.8 273.0 269.9 236.7 4G 330.9 252.6 545.6 346.0 341.6 256.5 16G 436.3 243.8 705.2 458.3 463.9 268.8 64G 486.0 253.3 767.3 532.5 516.9 274.7 It's easy to see how cache effects dominate the tlb walk. The only way hardware can reduce this is by increasing cache sizes dramatically. -- error compiling committee.c: too many arguments to function -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org