From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:34777) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z6jCH-0000rF-13 for qemu-devel@nongnu.org; Sun, 21 Jun 2015 13:38:22 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1Z6jCC-0000AY-VC for qemu-devel@nongnu.org; Sun, 21 Jun 2015 13:38:20 -0400 Received: from mout.web.de ([212.227.17.11]:51687) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1Z6jCC-0000AA-Kd for qemu-devel@nongnu.org; Sun, 21 Jun 2015 13:38:16 -0400 Message-ID: <5586F67E.5010708@web.de> Date: Sun, 21 Jun 2015 19:38:06 +0200 From: Jan Kiszka MIME-Version: 1.0 References: <55740B9C.6030107@web.de> <20150618202159.GK3874@thinpad.lan.raisama.net> In-Reply-To: <20150618202159.GK3874@thinpad.lan.raisama.net> Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="Bdb72pEX4wTL1MbQEE6ViCPihHRoi9nwT" Subject: Re: [Qemu-devel] [PATCH v5] i386: Introduce ARAT CPU feature List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Eduardo Habkost Cc: Paolo Bonzini , Marcelo Tosatti , qemu-devel , kvm , "Michael S. Tsirkin" This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --Bdb72pEX4wTL1MbQEE6ViCPihHRoi9nwT Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable On 2015-06-18 22:21, Eduardo Habkost wrote: > On Sun, Jun 07, 2015 at 11:15:08AM +0200, Jan Kiszka wrote: >> From: Jan Kiszka >> >> ARAT signals that the APIC timer does not stop in power saving states.= >> As our APICs are emulated, it's fine to expose this feature to guests,= >> at least when asking for KVM host features or with CPU types that >> include the flag. The exact model number that introduced the feature i= s >> not known, but reports can be found that it's at least available since= >> Sandy Bridge. >> >> Signed-off-by: Jan Kiszka >=20 > The code looks good now, but: what are the real consequences of > enabling/disabling the flag? What exactly guests use it for? >=20 > Isn't this going to make guests have additional expectations about the > APIC timer that may be broken when live-migrating or pausing the VM? ARAT only refers to stopping of the timer in certain power states (which we do not even emulate IIRC). In that case, the OS is under risk of sleeping forever, thus need to look for a different wakeup source. Live-migration or VM pausing are external effects on all timers of the guest, not only the APIC. However, none of them cause a wakeup miss - provided the host decides to resume the guest eventually. Jan --Bdb72pEX4wTL1MbQEE6ViCPihHRoi9nwT 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 iEYEARECAAYFAlWG9n4ACgkQitSsb3rl5xRfQgCgz25nNT7qR17yZsEvXW4RhmUR VYAAniVGkLbfDD3x5+oBNvauKQc7hKnh =Zi8A -----END PGP SIGNATURE----- --Bdb72pEX4wTL1MbQEE6ViCPihHRoi9nwT--