From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jan Kiszka Subject: Re: KVM handling external interrupts Date: Thu, 07 Jun 2012 12:48:51 +0200 Message-ID: <4FD08713.8090401@web.de> References: <4FD062BC.5090703@web.de> <4FD08113.9080709@web.de> Mime-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="------------enig1045C64D3751DC113A799D2B" Cc: Abel Gordon , Alex Landau , Dan Tsafrir , sheng qiu , kvm , Muli Ben-Yehuda , Nadav Amit To: Nadav Har'El Return-path: Received: from mout.web.de ([212.227.17.12]:55467 "EHLO mout.web.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760567Ab2FGKsz (ORCPT ); Thu, 7 Jun 2012 06:48:55 -0400 In-Reply-To: Sender: kvm-owner@vger.kernel.org List-ID: This is an OpenPGP/MIME signed message (RFC 2440 and 3156) --------------enig1045C64D3751DC113A799D2B Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable On 2012-06-07 12:34, Nadav Har'El wrote: >> - You discuss interrupt delivery without stating that you have MSIs i= n >> mind. Some aspects may be helpful for legacy interrupts as well, bu= t >> you obviously can't achieve exit-less operation there. Not an issue= , >> should just be made clear. >=20 > Can you eleborate on why exit-less operation cannot be achieved without= > MSI? Doesn't the VMCS flag to avoid exiting on external interrupts > apply to any interrupts? Or something else won't work? The guest needs to interact with the IOAPIC. And this resource is shared between host and guest. It can't be passed through. >=20 > In any case, you're right that our implementation and tests all used > MSI. >=20 >>> need paravirtualize the guest: no if you have x2APIC. >> >> ...and the guest makes use of it. This excludes older OSes. When did >> Windows start to use it? >=20 > Iff you can't use x2APIC, and don't want to paravirtualize Often, it is more about "... _can't_ paravirtualize". :) > the guest, you still get exit-less interrupt *delivery*, which as we > showed in the benchmarks, gets you more than half of the performance > improvement (although with newer KVM's improvement in EOI emulation > performance, the over-half improvement should be somewhat less pronounc= ed). Yes, I understood this, and I think looking at direct delivery would be a good first step to check if this could eventually become an upstream feature. It should even be beneficial for legacy interrupts. Jan --------------enig1045C64D3751DC113A799D2B Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.16 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/ iEYEARECAAYFAk/QhxMACgkQitSsb3rl5xTM+ACgg4I2gPe5284MrPFA/f2A9n/I uAEAoLHQ3tJOOgqhM/qIwo3L+Z6RwteV =NPXn -----END PGP SIGNATURE----- --------------enig1045C64D3751DC113A799D2B--