From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760328AbcBYMef (ORCPT ); Thu, 25 Feb 2016 07:34:35 -0500 Received: from mx1.redhat.com ([209.132.183.28]:56083 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759849AbcBYMee (ORCPT ); Thu, 25 Feb 2016 07:34:34 -0500 Date: Thu, 25 Feb 2016 13:34:29 +0100 From: Peter Krempa To: Radim =?utf-8?B?S3LEjW3DocWZ?= Cc: Paolo Bonzini , linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Yuki Shibuya , Rik van Riel Subject: Re: [PATCH v2 01/14] KVM: x86: change PIT discard tick policy Message-ID: <20160225123429.GD5757@andariel.pipo.sk> References: <1455736496-374-1-git-send-email-rkrcmar@redhat.com> <1455736496-374-2-git-send-email-rkrcmar@redhat.com> <56C5EDA9.9030204@redhat.com> <20160218165608.GC18904@potion.brq.redhat.com> <56C6004F.2050105@redhat.com> <56C60579.5040003@redhat.com> <20160219144422.GA2456@potion.brq.redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="ieNMXl1Fr3cevapt" Content-Disposition: inline In-Reply-To: <20160219144422.GA2456@potion.brq.redhat.com> X-PGP-Key-ID: 0xD018682B X-PGP-Key-Fingerprint: D294 FF38 A6A2 BF40 6C75 5DEF 36EC 16AC D018 682B User-Agent: Mutt/1.5.24 (2015-08-30) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org --ieNMXl1Fr3cevapt Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Fri, Feb 19, 2016 at 15:44:23 +0100, Radim Kr=C4=8Dm=C3=A1=C5=99 wrote: > [Cc'd Peter, the last guy that touched timers in libvirt, because he > might know what tick policies are supposed to be.] I found the following RFC that describes the design of timer access in libvirt: http://www.redhat.com/archives/libvir-list/2010-March/msg00304.html >=20 > 2016-02-18 18:55+0100, Paolo Bonzini: > > On 18/02/2016 18:33, Paolo Bonzini wrote: > >> On 18/02/2016 17:56, Radim Kr=C4=8Dm=C3=A1=C5=99 wrote: > >>> 2016-02-18 17:13+0100, Paolo Bonzini: > >>>> On 17/02/2016 20:14, Radim Kr=C4=8Dm=C3=A1=C5=99 wrote: > >>>>> Discard policy uses ack_notifiers to prevent injection of PIT inter= rupts > >>>>> before EOI from the last one. > >>>>> > >>>>> This patch changes the policy to always try to deliver the interrup= t, > >>>>> which makes a difference when its vector is in ISR. > >>>>> Old implementation would drop the interrupt, but proposed one injec= ts to > >>>>> IRR, like real hardware would. > >>>> > >>>> This seems like what libvirt calls the "merge" policy: > >>> > >>> Oops, I never looked beyond QEMU after seeing that the naming in libv= irt > >>> doesn't even match ... > >>> > >>> I think the policy that KVM implements (which I call discard) is "del= ay" > >>> in libvirt. (https://libvirt.org/formatdomain.html#elementsTime) >=20 > (I looked at libvirt code, but couldn't find any use of merge or discard > policies, so please bear with me as I disagree wherever it's possible.) Indeed, it looks like it never was implemented. Unfortunately i'm not able to assist more in this case. Peter --ieNMXl1Fr3cevapt Content-Type: application/pgp-signature; name="signature.asc" Content-Description: Digital signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iQIcBAEBCAAGBQJWzvTVAAoJEDbsFqzQGGgrvOMP/2zjZ9BKG1KfwoNh/i+UeUzs J5YSyhp1I8+83KW5YXkiCwTlf3uD7eAkmGz20CQeX42lfkcxCjP7JszlLPvkezke kviAmMAburDmuXHd4tPQz7K+baPMF2SgiDHZ23YufYrhVOwH1cdlvMRvsm3G7D5u 9xlEaCd8lZJI6TV9p4bUmrLacaY/uB0ptzOYKi5boeWag2mkyHGfS+cy3eqCxrZx WdP5hfEQgmDdcvPsnCkai3kVUJmlZzT5rrMua+SzjCjw9wJcK6TsbyJigUWNfPj1 QPw9QkE3KaXEOfHkM6TLQItYf8Mt6uRubhDvsT+pBMPTVCF/UVSPSmHgPQ+8XMOE 2u8CjkQIY7qmBDBEavpDJuGnv9XlZmMPFAT5JPPGLip9oHrisj47TY/6ATaa5s3k bMa/86/NSJVKMHR3S38VzN3e9MgIIkD2JT5WdwuKm8Y3Vr6p4yqM59siQFnXRhqH 6zCqTwuAO+DiVakTqK9GSBSIoNHDkNyj3b7spSo6wHrYgIR7WdxY8JeCD57iTe36 tKpnWUEXH2aUljVrQr34AHcq1YIw0cp/vTmIIaBsm2bLkvvlIenLbR7SyKTctdO3 ApF7Mv+Pg+AblUma2ieDAebNNvQ4SsBSCFuowBlpauR1R58glo7LQnsocVboPtvC LWFAM5/5buCHJ/O3ySCv =mLEL -----END PGP SIGNATURE----- --ieNMXl1Fr3cevapt--