From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dario Faggioli Subject: Re: PV-vNUMA issue: topology is misinterpreted by the guest Date: Mon, 27 Jul 2015 15:23:15 +0200 Message-ID: <1438003395.5036.122.camel@citrix.com> References: <55AFAC34.1060606@oracle.com> <55B070ED.2040200@suse.com> <1437660433.5036.96.camel@citrix.com> <55B21364.5040906@suse.com> <1437749076.4682.47.camel@citrix.com> <55B25650.4030402@suse.com> <55B258C9.4040400@suse.com> <1437753509.4682.78.camel@citrix.com> <20150724160948.GA2067@l.oracle.com> <55B26570.1060008@suse.com> <20150724162911.GC2220@l.oracle.com> <55B26A45.2050402@suse.com> <55B26B84.1000101@oracle.com> <55B5B504.2030504@suse.com> <55B60DE7.1020300@suse.com> <55B611F1.80508@citrix.com> <55B61DA5.5030903@suse.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============5759268508208115700==" Return-path: Received: from mail6.bemta5.messagelabs.com ([195.245.231.135]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1ZJiNc-00072r-Ge for xen-devel@lists.xenproject.org; Mon, 27 Jul 2015 13:23:44 +0000 In-Reply-To: <55B61DA5.5030903@suse.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Juergen Gross Cc: Elena Ufimtseva , Wei Liu , George Dunlap , Andrew Cooper , George Dunlap , David Vrabel , Jan Beulich , "xen-devel@lists.xenproject.org" , Boris Ostrovsky List-Id: xen-devel@lists.xenproject.org --===============5759268508208115700== Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="=-P1+Hv3PGG3Dy33ze9VWV" --=-P1+Hv3PGG3Dy33ze9VWV Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Mon, 2015-07-27 at 14:01 +0200, Juergen Gross wrote: > On 07/27/2015 01:11 PM, George Dunlap wrote: > > Or alternately, if the user wants to give up on the "consolidation" > > aspect of virtualization, they can pin vcpus to pcpus and then pass in > > the actual host topology (hyperthreads and all). >=20 > There would be another solution, of course: >=20 > Support hyperthreads in the Xen scheduler via gang scheduling. While > this is not a simple solution, it is a fair one. Hyperthreads on one > core can influence each other rather much. With both threads always > running vcpus of the same guest the penalty/advantage would stay in the > same domain. The guest could make really sensible scheduling decisions > and the licensing would still work as desired. >=20 This is interesting indeed, but I much rather see it as something orthogonal, which may indeed bring benefits in some of the scenarios described here, but should not be considered *the* solution. Implementing, enabling and asking users to use something like this will impact the system behavior and performance, in ways that may not be desirable for all use cases. So, while I do think that this may be something nice to have and offer, trying to use it for solving the problem we're debating here would make things even more complex to configure. Also, this would take care of HT related issues, but what about cores (as in 'should vcpus be cores of sockets or full sockets') and !HT boxes (like AMD)? Not to mention, as you say yourself, that it's not easy to implement. > Just an idea, but maybe worth to explore further instead of tweaking > more and more bits to make the virtual system somehow act sane. >=20 Sure, and it it's interesting indeed, for a bunch or reasons and purposes (as Tim is also noting). Not so much --or at least not necessarily-- for this one, IMO. Regards, Dario --=20 <> (Raistlin Majere) ----------------------------------------------------------------- Dario Faggioli, Ph.D, http://about.me/dario.faggioli Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK) --=-P1+Hv3PGG3Dy33ze9VWV Content-Type: application/pgp-signature; name="signature.asc" Content-Description: This is a digitally signed message part Content-Transfer-Encoding: 7bit -----BEGIN PGP SIGNATURE----- Version: GnuPG v2 iEYEABECAAYFAlW2MMMACgkQk4XaBE3IOsRG5wCfSr0aKtGEsO4ZDhfs6DRVDa1x RZEAoKDYrTk0tCJovGQauJ2TuWQ6QRIf =IdPq -----END PGP SIGNATURE----- --=-P1+Hv3PGG3Dy33ze9VWV-- --===============5759268508208115700== Content-Type: text/plain; charset="us-ascii" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Content-Disposition: inline _______________________________________________ Xen-devel mailing list Xen-devel@lists.xen.org http://lists.xen.org/xen-devel --===============5759268508208115700==--