Am I correct in reading the code that there is no "noht" (turn off hyperthreading) option in Xen (except in powerpc)? This was a surprise to me as I've seen it documented in various places and I recently suggested it as a diagnostic to a customer. ==================================If Xen could save time in a bottle / then clocks wouldn't virtually skew / It would save every tick / for VMs that aren't quick / and Xen then would send them anew (with apologies to the late great Jim Croce) _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
It disappeared a long time ago, possibly by accident, but noone has yet complained. -- Keir On 21/4/08 22:42, "Dan Magenheimer" <dan.magenheimer@oracle.com> wrote:> Am I correct in reading the code that there is no "noht" > (turn off hyperthreading) option in Xen (except in powerpc)? > This was a surprise to me as I''ve seen it documented in > various places and I recently suggested it as a diagnostic > to a customer. > > ==================================> If Xen could save time in a bottle / then clocks wouldn''t virtually skew / > It would save every tick / for VMs that aren''t quick / > and Xen then would send them anew > (with apologies to the late great Jim Croce) > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xensource.com > http://lists.xensource.com/xen-devel_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
> but noone has yet complained.Perhaps that''s because the common use case is "try noht and see if it makes any difference". Guess what? Since "noht" is silently ignored, it *doesn''t* make any difference. ;-) There are many xen-devel and xen-users postings (since it disappeared) that indicate that noht is assumed to work. Even Mark Williamson has a 2007 posting that implies that it should work. Also, I''ll bet the fraction of machines running Xen today that both support hyperthreading (and have it turned on in the BIOS) is very small. But if rumors are true, that may change over the next couple of years. Any comments or concerns from CPU vendors?> -----Original Message----- > From: Keir Fraser [mailto:keir.fraser@eu.citrix.com] > Sent: Monday, April 21, 2008 4:54 PM > To: dan.magenheimer@oracle.com; Xen-Devel (E-mail) > Subject: Re: [Xen-devel] No noht? > > > It disappeared a long time ago, possibly by accident, but > noone has yet > complained. > > -- Keir > > On 21/4/08 22:42, "Dan Magenheimer" > <dan.magenheimer@oracle.com> wrote: > > > Am I correct in reading the code that there is no "noht" > > (turn off hyperthreading) option in Xen (except in powerpc)? > > This was a surprise to me as I''ve seen it documented in > > various places and I recently suggested it as a diagnostic > > to a customer. > > > > ==================================> > If Xen could save time in a bottle / then clocks wouldn''t > virtually skew / > > It would save every tick / for VMs that aren''t quick / > > and Xen then would send them anew > > (with apologies to the late great Jim Croce) > > _______________________________________________ > > Xen-devel mailing list > > Xen-devel@lists.xensource.com > > http://lists.xensource.com/xen-devel > > >_______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel
> Perhaps that''s because the common use case is "try > noht and see if it makes any difference". Guess what? > Since "noht" is silently ignored, it *doesn''t* make any > difference. ;-) There are many xen-devel and xen-users > postings (since it disappeared) that indicate that noht > is assumed to work. Even Mark Williamson has a 2007 > posting that implies that it should work.Hrmmm. I often poke into the sourcecode to check regarding options I''m about to tell people to use; I probably didn''t do that for noht so it may still have been around at the time. I can''t remember it going away; I don''t imagine it would be very difficult to reintroduce, if we figure out where / why it went away in the first place! Failing that, it should get de-documented from anywhere it''s currently mentioned...> Also, I''ll bet the fraction of machines running Xen > today that both support hyperthreading (and have it > turned on in the BIOS) is very small. But > if rumors are true, that may change over the > next couple of years.Yup, it sounds like HT is on its way back to Intel machines. Cheers, Mark> Any comments or concerns from CPU vendors? > > > -----Original Message----- > > From: Keir Fraser [mailto:keir.fraser@eu.citrix.com] > > Sent: Monday, April 21, 2008 4:54 PM > > To: dan.magenheimer@oracle.com; Xen-Devel (E-mail) > > Subject: Re: [Xen-devel] No noht? > > > > > > It disappeared a long time ago, possibly by accident, but > > noone has yet > > complained. > > > > -- Keir > > > > On 21/4/08 22:42, "Dan Magenheimer" > > > > <dan.magenheimer@oracle.com> wrote: > > > Am I correct in reading the code that there is no "noht" > > > (turn off hyperthreading) option in Xen (except in powerpc)? > > > This was a surprise to me as I''ve seen it documented in > > > various places and I recently suggested it as a diagnostic > > > to a customer. > > > > > > ==================================> > > If Xen could save time in a bottle / then clocks wouldn''t > > > > virtually skew / > > > > > It would save every tick / for VMs that aren''t quick / > > > and Xen then would send them anew > > > (with apologies to the late great Jim Croce) > > > _______________________________________________ > > > Xen-devel mailing list > > > Xen-devel@lists.xensource.com > > > http://lists.xensource.com/xen-devel > > _______________________________________________ > Xen-devel mailing list > Xen-devel@lists.xensource.com > http://lists.xensource.com/xen-devel-- Push Me Pull You - Distributed SCM tool (http://www.cl.cam.ac.uk/~maw48/pmpu/) _______________________________________________ Xen-devel mailing list Xen-devel@lists.xensource.com http://lists.xensource.com/xen-devel