Re: Guest TSC and Xen (Intel and AMD feedback please)

[Dave Winchell <dwinchell@virtualiron.com>]

Hi Li,

Shouldn't this

+ regs->eax = tsc & 0xffff;
+ regs->edx = tsc >> 32 & 0xffff;

be

+ regs->eax = tsc & 0xffffffff;
+ regs->edx = tsc >> 32 & 0xffffffff;

Thanks,
Dave


Zhang, Li wrote:

>Hi, Dan
>Please ignore previous comments. The above attachment is OK. Sorry for that. :(
>
>  
>
>> -----Original Message-----
>> From: xen-devel-bounces@lists.xensource.com
>> [mailto:xen-devel-bounces@lists.xensource.com] On Behalf Of Zhang, Li
>> Sent: Tuesday, July 08, 2008 2:58 PM
>> To: dan.magenheimer@oracle.com; 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@lists.xensource.com
>> >  [mailto:xen-devel-bounces@lists.xensource.com] On Behalf Of Zhang, Li
>> >  Sent: Tuesday, July 08, 2008 2:49 PM
>> >  To: dan.magenheimer@oracle.com; 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@oracle.com]
>> >  >  Sent: Tuesday, July 08, 2008 11:34 AM
>> >  >  To: Zhang, Li; Xen-Devel (E-mail)
>> >  >  Cc: Tian, Kevin; dan.magenheimer@oracle.com
>> >  >  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@intel.com]
>> >  >  > Sent: Monday, July 07, 2008 9:00 PM
>> >  >  > To: dan.magenheimer@oracle.com; 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@oracle.com'; '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@oracle.com'; 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@oracle.com]
>> >  >  > >  >  >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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