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: Fri, 17 Jul 2015 09:27:55 +0200 Message-ID: <1437118075.23656.25.camel@citrix.com> References: <1437042762.28251.18.camel@citrix.com> <55A7A7F40200007800091D60@mail.emea.novell.com> <55A78DF2.1060709@citrix.com> <20150716152513.GU12455@zion.uk.xensource.com> <55A7D17C.5060602@citrix.com> <55A7D2CC.1050708@oracle.com> <55A7F7F40200007800092152@mail.emea.novell.com> <55A7DE45.4040804@citrix.com> <55A7E2D8.3040203@oracle.com> <55A8B83802000078000924AE@mail.emea.novell.com> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============5513893922322506093==" Return-path: Received: from mail6.bemta14.messagelabs.com ([193.109.254.103]) by lists.xen.org with esmtp (Exim 4.72) (envelope-from ) id 1ZG046-0006Mk-Gs for xen-devel@lists.xenproject.org; Fri, 17 Jul 2015 07:28:14 +0000 In-Reply-To: <55A8B83802000078000924AE@mail.emea.novell.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: Jan Beulich Cc: Elena Ufimtseva , Wei Liu , Andrew Cooper , David Vrabel , "xen-devel@lists.xenproject.org" , Boris Ostrovsky List-Id: xen-devel@lists.xenproject.org --===============5513893922322506093== Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="=-h95FZA6xJzq+A+ykMVdp" --=-h95FZA6xJzq+A+ykMVdp Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable On Fri, 2015-07-17 at 07:09 +0100, Jan Beulich wrote: > >>> On 16.07.15 at 18:59, wrote: > > And in general (both for PV and HVM) --- is there any reason to expose= =20 > > CPU topology at all? I can see it being useful if VCPUs are pinned but= =20 > > if they are not then it can make performance worse. >=20 > Indeed=20 > Indeed indeed. :-) And in fact, this is even independent from vNUMA. Yet, I remember we were discussing about this since the beginning of vNUMA work, back when it was Elena doing it, but the it seems we all forgot... Sorry for that! :-/ I seriously think we should do something about this as, while in a non vNUMA setup it can certainly cause weird/inconsistent performance, in a vNUMA one, as shown, it's quite a hige mess. > - that's what our kernels have been doing for years, and > it seems like someone over here is now looking into whether this > could be done in pv-ops too (without too much uglification). >=20 That would be great, IMO. I'd be up for helping with this, but I know next to nothing about CPUID, so that would require some setup time. If, at least, you could keep me in the loop it would be great. In the meanwhile, what should we do? Document this? How? "don't use vNUMA with PV guest in SMT enabled systems" seems a bit harsh... Is there a workaround we can put in place/suggest? Regards, Dario --=20 <> (Raistlin Majere) ----------------------------------------------------------------- Dario Faggioli, Ph.D, http://about.me/dario.faggioli Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK) --=-h95FZA6xJzq+A+ykMVdp 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 iEYEABECAAYFAlWornwACgkQk4XaBE3IOsTvEwCeM657hBLNLm7udAAHK6K1iBNs +DkAoIDLTcuFAV+OCZR5a+A39iwT7IPo =CkqA -----END PGP SIGNATURE----- --=-h95FZA6xJzq+A+ykMVdp-- --===============5513893922322506093== 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 --===============5513893922322506093==--