From: Olaf Hering Subject: Re: [PATCH v3] new config option vtsc_tolerance_khz to avoid TSC emulation Date: Tue, 6 Mar 2018 12:32:42 +0100 Message-ID: <20180306123242.44f69b41.olaf@aepfle.de> References: <20180306104133.22106-1-olaf@aepfle.de> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============3168183267951956349==" Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" To: Andrew Cooper Cc: Stefano Stabellini , Wei Liu , George Dunlap , Tim Deegan , Ian Jackson , Marek =?UTF-8?B?TWFy?= =?UTF-8?B?Y3p5a293c2tpLUfDs3JlY2tp?= , xen-devel@lists.xen.org, Julien Grall , Jan Beulich , Daniel De Graaf List-Id: xen-devel@lists.xenproject.org --===============3168183267951956349== Content-Type: multipart/signed; micalg=pgp-sha1; boundary="Sig_/2c/ecJP+3/e43JOldwbXljA"; protocol="application/pgp-signature" --Sig_/2c/ecJP+3/e43JOldwbXljA Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable Am Tue, 6 Mar 2018 11:07:54 +0000 schrieb Andrew Cooper : > > One option to avoid the TSC option is to run domUs with tsc_mode=3Dnati= ve. > > This has the drawback that migrating a domU from a "2.3GHz" class host > > to a "2.4GHz" class host may change the rate at wich the TSC counter > > increases, the domU may not be prepared for that. =20 >=20 > Given that you identify this specifically, why do you think this change > is safe or sensible in the first place?=C2=A0 If using the options here, = time > will definitely drift in the VM after migrate. This option is a variant of tsc_mode=3Ddefault for different hosts, and tsc_mode=3Dnative for identical hosts. I think the tsc_mode can not be adjusted for running domUs. So it gives some control to the host admin about how to handle the drift. Olaf --Sig_/2c/ecJP+3/e43JOldwbXljA Content-Type: application/pgp-signature Content-Description: Digitale Signatur von OpenPGP -----BEGIN PGP SIGNATURE----- iF0EARECAB0WIQSkRyP6Rn//f03pRUBdQqD6ppg2fgUCWp58WgAKCRBdQqD6ppg2 fnm1AJ9UEdFHXDr+eXjuljOxlU9tVLQiEQCg3pE+RTiIqNhoL2ZB1UcCouJyPps= =mUAs -----END PGP SIGNATURE----- --Sig_/2c/ecJP+3/e43JOldwbXljA-- --===============3168183267951956349== Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: base64 Content-Disposition: inline X19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX19fX18KWGVuLWRldmVs IG1haWxpbmcgbGlzdApYZW4tZGV2ZWxAbGlzdHMueGVucHJvamVjdC5vcmcKaHR0cHM6Ly9saXN0 cy54ZW5wcm9qZWN0Lm9yZy9tYWlsbWFuL2xpc3RpbmZvL3hlbi1kZXZlbA== --===============3168183267951956349==--