RE: [Xen-devel] Guest TSC and Xen (Intel and AMD feedback please)

["Dan Magenheimer" <dan.magenheimer@xxxxxxxxxx>]

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
> >  >  >  >
> >
> >  _______________________________________________
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> >  Xen-devel@xxxxxxxxxxxxxxxxxxx
> >  http://lists.xensource.com/xen-devel
> 
>

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