From mboxrd@z Thu Jan 1 00:00:00 1970 From: "SourceForge.net" Subject: [ kvm-Bugs-1906204 ] AMD NPT causes performance degradation Date: Wed, 27 Aug 2008 11:41:11 +0000 Message-ID: Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" To: noreply@sourceforge.net Return-path: Received: from ch3.sourceforge.net ([216.34.181.60]:35898 "EHLO ch3.sourceforge.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755092AbYH0LlO (ORCPT ); Wed, 27 Aug 2008 07:41:14 -0400 Sender: kvm-owner@vger.kernel.org List-ID: Bugs item #1906204, was opened at 2008-03-03 13:45 Message generated for change (Comment added) made by avik You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=893831&aid=1906204&group_id=180599 Please note that this message will contain a full copy of the comment thread, including the initial issue submission, for this request, not just the latest update. Category: None Group: None Status: Open Resolution: None Priority: 5 Private: No Submitted By: Technologov (technologov) Assigned to: Nobody/Anonymous (nobody) Summary: AMD NPT causes performance degradation Initial Comment: Platform: F7/x64, AMD Barcelona K10, KVM-61. Guest: Windows XP SP2. By default, the new Nested Page Tables is enabled, which should accelerate guests. While it *does* accelerate guests in some areas, particularly guest OS setup time dropped by 20% - which is great, but in other areas I see performance degradation. For example: Passmark PerformanceTest v6.1 shows 2D Graphics Marks: 78.6 (without NPT) 2D Graphics Marks: 18.9 (with NPT) NPT was disabled using: # rmmod kvm-amd # modprobe kvm-amd npt=0 # dmesg | tail and all the graphics feel more sluggish, and way slower. I have used SDL rendering. -Alexey, 03.03.2008. ---------------------------------------------------------------------- >Comment By: Avi Kivity (avik) Date: 2008-08-27 14:41 Message: Logged In: YES user_id=539971 Originator: NO Make sure your host has the latest BIOS. ---------------------------------------------------------------------- Comment By: Marco Menardi (markit) Date: 2008-08-26 22:59 Message: Logged In: YES user_id=113918 Originator: NO Same here, XP has a noticeable slow down. Was faster with my AMD X2 that is with 4 core Phenom. WIth npt=0 is fast again (as with X2 or better). Tried with kvm 70...73, debian Sid 64 as host ---------------------------------------------------------------------- Comment By: Anthony Liguori (aliguori) Date: 2008-03-25 00:03 Message: Logged In: YES user_id=120449 Originator: NO I am able to reproduce this although the results aren't as extreme. The biggest impact is coming from the passmark 2D Graphics Filled Rectangles test. Only about 40k exits are occurring while this benchmark is being run. It's not impacted by the use of large pages. Still investigating. ---------------------------------------------------------------------- Comment By: Technologov (technologov) Date: 2008-03-03 17:25 Message: Logged In: YES user_id=1839746 Originator: YES Yes, those numbers are always reproducible, even with reloading KVM base module too. Just try it for yourself, the benchmark is shareware (free for 30 days) - but VMs rarely live any longer anyways :) link: http://www.passmark.com/ -Alexey, 03.03.2008. ---------------------------------------------------------------------- Comment By: Joerg Roedel (jroedel) Date: 2008-03-03 16:40 Message: Logged In: YES user_id=2019182 Originator: NO Reloading the KVM-AMD module does not disable NPT completly. You have to reload the KVM base module too. Can you reproduce your numbers if you reload both and disable NPT? ---------------------------------------------------------------------- You can respond by visiting: https://sourceforge.net/tracker/?func=detail&atid=893831&aid=1906204&group_id=180599