The attached patch adds a new Xen boot option "softtsc" that
causes all hvm domains to trap and emulate all rdtsc instructions
and fetch Xen system time instead of the hardware tsc. As
a result, the processor will appear to be running at 1000.xyz MHz
(where xyz indicates some fraction that seems to vary slightly
across different boots). I've also added a line of output to
"xm debug-key t" to report softsc and tsc-related CPU features.
(Keir, though 3.3 functionality freeze is past, this is more of a
diagnostic aid and defaults off, so I don't know if you would
consider it for 3.3.)
Signed-off-by: Dan Magenheimer <dan.magenheimer@xxxxxxxxxx>
Dan
P.S. Thanks to Li Zhang for coding the foundation for this patch.
Li, do you want to provide a signed-off-by line too?
> -----Original Message-----
> From: Dan Magenheimer [mailto:dan.magenheimer@xxxxxxxxxx]
> Sent: Tuesday, July 08, 2008 6:30 PM
> To: 'Zhang, Li'; 'Xen-Devel (E-mail)'
> Cc: 'Tian, Kevin'
> Subject: RE: [Xen-devel] Guest TSC and Xen (Intel and AMD
> feedback please)
>
>
> Looks great! I am continuing to code and test. Some
> preliminary results:
>
> 1) Substituting hvm_get_guest_time() for hvm_get_guest_tsc()
> seems to just work! The hvm
> guest believes it is running on a 1000.185 MHz clock.
>
> 2) On my test box, a guest rdtsc without softtsc takes about
> 30ns. With softtsc,
> rdtsc takes about 1us.
>
> 3) On my user-land test program, I am seeing rare "Time goes
> backwards", even with
> hvm_get_guest_time(). I'm trying to track this down.
>
> Dan
>
> > -----Original Message-----
> > From: Zhang, Li [mailto:li.zhang@xxxxxxxxx]
> > Sent: Tuesday, July 08, 2008 3:47 AM
> > To: Zhang, Li; dan.magenheimer@xxxxxxxxxx; Xen-Devel (E-mail)
> > Cc: Tian, Kevin
> > Subject: RE: [Xen-devel] Guest TSC and Xen (Intel and AMD
> > feedback please)
> >
> >
> > Hi, Dan
> > Please ignore previous comments. The above attachment is OK.
> > Sorry for that. :(
> >
> > > -----Original Message-----
> > > From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
> > > [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On Behalf
> > Of Zhang, Li
> > > Sent: Tuesday, July 08, 2008 2:58 PM
> > > To: dan.magenheimer@xxxxxxxxxx; Xen-Devel (E-mail)
> > > Cc: Tian, Kevin
> > > Subject: RE: [Xen-devel] Guest TSC and Xen (Intel and AMD
> > feedback please)
> > >
> > > In fact, the issue is from guest. In the guest's terminal,
> > it shows that "your
> > > time source seems to be instable..."
> > >
> > > > -----Original Message-----
> > > > From: xen-devel-bounces@xxxxxxxxxxxxxxxxxxx
> > > > [mailto:xen-devel-bounces@xxxxxxxxxxxxxxxxxxx] On
> > Behalf Of Zhang, Li
> > > > Sent: Tuesday, July 08, 2008 2:49 PM
> > > > To: dan.magenheimer@xxxxxxxxxx; Xen-Devel (E-mail)
> > > > Cc: Tian, Kevin
> > > > Subject: RE: [Xen-devel] Guest TSC and Xen (Intel and
> > AMD feedback please)
> > > >
> > > > Hi, Dan
> > > >
> > > > This is the patch which I think it has been completed
> > VT. But there is an
> > > > instable issue. The reason may be from that this
> > interception is not bound
> > > > to timer mode yet.
> > > >
> > > > Thanks
> > > > --Li
> > > >
> > > > > -----Original Message-----
> > > > > From: Dan Magenheimer [mailto:dan.magenheimer@xxxxxxxxxx]
> > > > > Sent: Tuesday, July 08, 2008 11:34 AM
> > > > > To: Zhang, Li; Xen-Devel (E-mail)
> > > > > Cc: Tian, Kevin; dan.magenheimer@xxxxxxxxxx
> > > > > Subject: RE: [Xen-devel] Guest TSC and Xen (Intel
> > and AMD feedback
> > > please)
> > > > >
> > > > > Thanks Kevin and Li --
> > > > >
> > > > > A couple of questions:
> > > > >
> > > > > 1) If the EXITING flag to be set in vmcs.c is to be
> > controlled by a xen
> > > > boot
> > > > > option, would this work:
> > > > >
> > > > > static int opt_softtsc = 0;
> > > > > boolean_param("softtsc", opt_softtsc);
> > > > > :
> > > > > min = /* original code */
> > > > > if (opt_softtsc) min |= CPU_BASED_RDTSC_EXITING;
> > > > >
> > > > > 2) In vmx_rdtsc_intercept(/* need regs as param*/)
> > if we change the
> > > > > rdtscll(tsc) to be tmptsc = hvm_get_guest_tsc() and
> > then set regs->edx
> > > amd
> > > > > regs->eax from tmptsc, are we almost done?
> > > > >
> > > > > 3) Des Linux or Windows use the CR4.TSD flag and, if
> > so, what code gets
> > > > called
> > > > > to force the trap?
> > > > >
> > > > > 4) Does Linux or Windows use RDMSR/WRMSR of tsc? Is
> > there already code
> > > > > somewhere to emulate WRMSR of tsc?
> > > > >
> > > > > Sorry I am not very familar with the details of the
> > ia32 instruction
> > > set.
> > > > >
> > > > > Thanks,
> > > > > Dan
> > > > >
> > > > > > -----Original Message-----
> > > > > > From: Zhang, Li [mailto:li.zhang@xxxxxxxxx]
> > > > > > Sent: Monday, July 07, 2008 9:00 PM
> > > > > > To: dan.magenheimer@xxxxxxxxxx; Xen-Devel (E-mail)
> > > > > > Cc: Tian, Kevin
> > > > > > Subject: RE: [Xen-devel] Guest TSC and Xen (Intel and AMD
> > > > > > feedback please)
> > > > > >
> > > > > >
> > > > > > Hi, Dan
> > > > > > This seems not to be enough. I will cook another patch.
> > > > > >
> > > > > > > -----Original Message-----
> > > > > > > From: Zhang, Li
> > > > > > > Sent: Tuesday, July 08, 2008 10:28 AM
> > > > > > > To: Tian, Kevin; 'dan.magenheimer@xxxxxxxxxx';
> > 'Xen-Devel
> > > (E-mail)'
> > > > > > > Subject: RE: [Xen-devel] Guest TSC and Xen
> > (Intel and AMD
> > > > > > feedback please)
> > > > > > >
> > > > > > > Hi, Dan
> > > > > > >
> > > > > > > I just add some code to produce vmexit. The function
> > > > > > vmx_rdtsc_intercept()
> > > > > > > is not completed. It is needed to add some code
> > to get the
> > > > > > guest tsc.
> > > > > > >
> > > > > > > Thanks
> > > > > > > --Li
> > > > > > >
> > > > > > > > -----Original Message-----
> > > > > > > > From: Tian, Kevin
> > > > > > > > Sent: Tuesday, July 08, 2008 9:39 AM
> > > > > > > > To: 'dan.magenheimer@xxxxxxxxxx';
> Xen-Devel (E-mail)
> > > > > > > > Cc: Zhang, Li
> > > > > > > > Subject: RE: [Xen-devel] Guest TSC and Xen
> (Intel and
> > > > > > AMD feedback please)
> > > > > > > >
> > > > > > > > >From: Dan Magenheimer
> > [mailto:dan.magenheimer@xxxxxxxxxx]
> > > > > > > > >Sent: 2008年7月5日 1:32
> > > > > > > > >
> > > > > > > > >> >Is this something that you (or Intel
> in general)
> > > > > > could look at?
> > > > > > > > >> >I would be happy to participate but I
> > don't think I
> > > > > > understand
> > > > > > > > >> >VT well enough. Once the trap occurs,
> I suppose
> > > > > > Xen system time
> > > > > > > > >> >could be used as the virtual TSC,
> > possibly scaled up.
> > > > > > > > >> >
> > > > > > > > >>
> > > > > > > > >> There should be tiny related to VT, as
> > only turning
> > > > > > on some bit to
> > > > > > > > >> allow RDTSC trapping and then the rest
> > stuff should be common
> > > > > > > > >> how to handle it. We'll take a look, but can't
> > > > > > commit the time due
> > > > > > > > >> to other scheduled bandwidth. But if
> you'd like to
> > > > > > jump in early
> > > > > > > > >> we definitely can help with VT side.
> > > > > > > > >
> > > > > > > > >If you can post a patch with code that:
> > > > > > > > >
> > > > > > > > >1) declares a boolean global variable: softtsc = 0
> > > > > > > > >2) if the variable is set, a rdtsc
> > instruction in any hvm
> > > > > > > > > domain causes a trap
> > > > > > > > >3) the trap handler just does a physical
> > rdtsc and returns
> > > > > > > > >
> > > > > > > > >then I could probably take it from there.
> > > > > > > >
> > > > > > > > OK, and Li in CC will take a look and bake a
> > patch for you.
> > > > > > > >
> > > > > > > > Thanks,
> > > > > > > > Kevin
> > > > > >
> > >
> > > _______________________________________________
> > > Xen-devel mailing list
> > > Xen-devel@xxxxxxxxxxxxxxxxxxx
> > > http://lists.xensource.com/xen-devel
> >
> >
softtsc.patch
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