From mboxrd@z Thu Jan 1 00:00:00 1970 From: Avi Kivity Subject: Re: [PATCH][UPDATE] shortcut for lightweight VM Exit Date: Mon, 30 Apr 2007 16:10:47 +0300 Message-ID: <4635EAD7.1030405@qumranet.com> References: <10EA09EFD8728347A513008B6B0DA77A015EDE49@pdsmsx411.ccr.corp.intel.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Cc: kvm-devel To: "Dong, Eddie" Return-path: In-Reply-To: <10EA09EFD8728347A513008B6B0DA77A015EDE49-wq7ZOvIWXbNpB2pF5aRoyrfspsVTdybXVpNB7YpNyf8@public.gmane.org> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org Errors-To: kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: kvm.vger.kernel.org Dong, Eddie wrote: > Avi Kivity wrote: > >> Dong, Eddie wrote: >> >>> This patch provides short cut handling for light weight VM Exit, >>> which can boost KB performance 11% under FC5 guest. >>> Any comments? >>> >> While the patch looks good, it kills FC6 x86_64 boot with a double >> fault. Guest kernel is 2.6.18-1.2798. dmesg says >> >> inject_page_fault: double fault 0x7fff79b58fd8 @ 0xffffffff8025cca1 >> >> > I think I know the reason, the SYSCALL_MASK & LSTAR update in guest > needs to > update the physical side MSR after this patch. With this update in > vmx_set_msr, > I get it up on a RHEL5U 64 bits guest but no time to check the detail > performance > gain yet. (will report after May day national holiday 5/1--5/8 in PRC) > > BTW, I have another patch in hand to further reduce MSR save/restore and > thus > improve performance more for lightweight VM Exit. Base on my observation > for FC5 32 bits > guest, 93% VM Exit will fall into the lightweight path. > > I measured 650 cycles saved from a total of 5300 before the patch. The patch had a bug where it would exit to userspace if need_resched() was true. This can reduce performance on a high context switch scenario (many virtual machines). I fixed that, and also a minor coding style issue, and applied. Enjoy your holiday :) -- error compiling committee.c: too many arguments to function ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/