From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: High vm-exit latencies during kvm boot-up/shutdown Date: Tue, 23 Oct 2007 11:08:42 +0200 Message-ID: <471DBA1A.2080108@web.de> References: <471D2D8C.1080202@web.de> <10EA09EFD8728347A513008B6B0DA77A02441127@pdsmsx411.ccr.corp.intel.com> <471D96DC.7070809@web.de> <10EA09EFD8728347A513008B6B0DA77A024414D9@pdsmsx411.ccr.corp.intel.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============0789462467==" Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org To: "Dong, Eddie" Return-path: In-Reply-To: <10EA09EFD8728347A513008B6B0DA77A024414D9-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 This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --===============0789462467== Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enigADFCBCB92A08E681C711E835" This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enigADFCBCB92A08E681C711E835 Content-Type: text/plain; charset=GB2312 Content-Transfer-Encoding: quoted-printable Dong, Eddie wrote: > =20 >=20 >> -----Original Message----- >> From: jan.kiszka-S0/GAf8tV78@public.gmane.org [mailto:jan.kiszka-S0/GAf8tV78@public.gmane.org]=20 >> Sent: 2007=C4=EA10=D4=C223=C8=D5 14:38 >> To: Dong, Eddie >> Cc: kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org >> Subject: Re: [kvm-devel] High vm-exit latencies during kvm=20 >> boot-up/shutdown >> >> Dong, Eddie wrote: >>> kvm-devel-bounces-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org wrote: >>>> Hi, >>>> >>>> I'm seeing fairly high vm-exit latencies (300-400 us)=20 >> during and only >>>> during qemu/kvm startup and shutdown on a Core2 T5500 in=20 >> 32-bit mode. >>>> It's most probably while the VM runs inside bios code.=20 >> During the rest >>>> of the time, while some Linux guest is running, the exit=20 >> latencies are >>>> within microseconds, thus perfectly fine for the real-time scenarios= >>>> I have in mind.=20 >>> How is this time spent? All in Qemu? >> Most probably. I have a function tracer installed, and it does not >> report any kernel function call between the begin of the asm block and= >> its end. >=20 > If the time is spent in Qemu, then it is possible to be that long=20 > since Qemu may read/write disk for the VM virtual disk. Clarification: I can't precisely tell what code is executed in VM mode, as I don't have qemu or that guest instrumented. I just see the kernel entering VM mode and leaving it again more than 300 us later. So I wonder why this is allowed while some external IRQ is pending. >=20 >>> Usually a kernel only VM Exit cost less than 1us. >> That's what I'm seeing for the rest as well. >> >> I have read that certain guest states do not allow preemptions by >> external interrupts (here it is the timer IRQ), but both >> GUEST_INTERRUPTIBILITY_INFO and GUEST_ACTIVITY_STATE are 0 on entry, >> e.g. Is there a way for the guest to trigger a non-preemptible SMM >> entry, and that without the kernel noticing it? >> > I am not aware of this possibility. > Eddie Jan --------------enigADFCBCB92A08E681C711E835 Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFHHbodniDOoMHTA+kRAjCmAJ0d5kK3sBYGyo14jIBLw+ufN8yAzQCfQNQB L2SlyR4HaCUqaiDtBvYUJ5Y= =yH9X -----END PGP SIGNATURE----- --------------enigADFCBCB92A08E681C711E835-- --===============0789462467== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ --===============0789462467== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ kvm-devel mailing list kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org https://lists.sourceforge.net/lists/listinfo/kvm-devel --===============0789462467==--