From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lloyd Dizon Subject: Re: [Xen-devel] Xen timekeeping best practices Date: Tue, 17 Apr 2012 11:35:03 +0200 Message-ID: References: <1334570256.14560.80.camel@zakaz.uk.xensource.com> <1334588223.14560.205.camel@zakaz.uk.xensource.com> <1334650567.11493.17.camel@dagon.hellion.org.uk> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: In-Reply-To: <1334650567.11493.17.camel@dagon.hellion.org.uk> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-users-bounces@lists.xen.org Errors-To: xen-users-bounces@lists.xen.org To: Ian Campbell Cc: "xen-users@lists.xen.org" , Todd Deshane , xen-devel mailing list , Remi Gacogne List-Id: xen-devel@lists.xenproject.org On Tue, Apr 17, 2012 at 10:16 AM, Ian Campbell wr= ote: > On Tue, 2012-04-17 at 08:41 +0100, Lloyd Dizon wrote: >> On Mon, Apr 16, 2012 at 4:57 PM, Ian Campbell = wrote: >> > On Mon, 2012-04-16 at 15:45 +0100, Lloyd Dizon wrote: >> >> On Mon, Apr 16, 2012 at 11:57 AM, Ian Campbell wrote: >> >> > >> >> > On Fri, 2012-04-13 at 18:22 +0100, Todd Deshane wrote: >> >> > > Adding Xen-devel. >> >> > > >> >> > > What are the current timekeeping best practices now? >> >> > >> >> > pvops kernels behave as if independent_wallclock =3D=3D 1, so the e= xisting >> >> > advice: >> >> > =A0 =A0 =A0 =A0set /proc/sys/xen/independent_wallclock to 1 and run= ntp on >> >> > =A0 =A0 =A0 =A0domU. >> >> > still applies. >> >> >> >> This also applies to Xen 4.0 (4.0.0) if I understood correctly? >> > >> > This is entirely a function of the guest kernel version and not the >> > hypervisor >> > >> >> If so and based on previous posts can we resume that this is what is >> >> recommended: >> > >> > If you s/Xen3/Classic XenoLinux Kernels/ and s/Xen4/Paravirt Ops Linux >> > Kernels/g then I think it is somewhat accurate, at least for the PV >> > line. >> > >> > I must confess I don't really know for the HVM line. I suspect that it >> > is actually: >> > >> > Classic XenoLinux -- no PV time source, independent_wallclock means >> > nothing, run NTP in the guest >> > >> > Paravirt ops kernels _without_ PV time PVHVM extensions -- no PV time >> > source, independent_wallclock means nothing, run NTP in the guest >> > >> > Paravirt ops kernels _with_ PV time PVHVM extensions -- PV time source, >> > independent_wallclock always =3D=3D 1, run NTP. >> > >> > So in short always run NTP in an HVM guest, regardless of the presence >> > or absence of PV time extensions >> >> I do not fully understand the difference yet between and Classic >> XenoLinux and Paravirt Ops Kernel (will dig the info later) > > Roughly: > > classic =3D=3D old out-of-tree Xen patches, static compile time support f= or > Xen. This is the old "2.6.18-xen.hg" tree and includes the "SuSE forward > port kernels" which are the classic patches kept up to date with recent > kernels. > > pvops =3D=3D patches in upstream Linux, dynamic support for Xen enabled at > kernel boot time. pvops supported domU from ~2.6.24 and dom0 from 3.0 > onwards. Thanks also found info here: http://wiki.xensource.com/xenwiki/XenDom0Kernels.html >> =A0but here >> is the resume: >> >> =A0 =A0 =A0 =A0---------------------------------------------------------= ---------------------------------------------------------- >> =A0 =A0 =A0 =A0| =A0Xen3: Classic XenoLinux Kern =A0 =A0 =A0 =A0 =A0 =A0= =A0 =A0 =A0 =A0 | >> =A0 =A0 Xen4: Paravirt Ops Linux Kern =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | >> ------------------------------------------------------------------------= -------------------------------------------------- >> =A0PV =A0 =A0| independent_wallclock =3D 0 or 1 =A0 =A0 =A0 =A0 =A0 =A0 = =A0 =A0 =A0 =A0| >> independent_wallclock =3D =A01 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 = =A0 =A0 =A0 =A0 =A0 =A0 =A0| >> ------------------------------------------------------------------------= -------------------------------------------------- >> =A0HVM =A0 | -> no PV timesource, no ind. wallclock, run NTP =A0 | -> w/= o PV >> time PVHVM extensions, no ind. wallclock, run NTP | >> =A0 =A0 =A0 =A0| =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0= =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 | -> PV >> time source, ind. wallclock always 1, run NTP =A0 =A0 =A0 =A0 | >> ------------------------------------------------------------------------= -------------------------------------------------- > > It got a bit mangled in transit but it looks reasonable. > > You should remove "Xen3" and "Xen4" from the titles since the hypervisor > version has no bearing on any of this. You can just as easily run a > pvops kernel on Xen3.x or a classic kernel on Xen4.x (and of course you > can mix and match those on a single host) > > The 3->4 major number transition was mostly just a version number bump, > it didn't indicate any major change in the API or anything like that -- > any PV kernel should run on any Xen from 3.0 onwards, right through to > 4.2 (and beyond). > >> Should we put this somewhere (wiki) until somebody else proves this is >> inaccurate ? > > Please do put it on the wiki, I think there was a reference to a page (a > FAQ?) further up thread which seems like as good a place as any to add > it. Done. Anybody please correct the information if inaccurate. http://wiki.xensource.com/wiki/Xen_FAQ_DomU#How_can_i_synchronize_a_dom0_cl= ock.3F