Re: [Xen-devel] Re: Fix for get_s_time()

[Dave Winchell <dwinchell@xxxxxxxxxxxxxxx>]

Keir,

Last nights run had the error in the 12 ppm range.
Here is the change we have been talking about.

-Dave

Dave Winchell wrote:

> Keir Fraser wrote:
>
> > On 24/4/08 17:04, "Dave Winchell" <dwinchell@xxxxxxxxxxxxxxx> wrote:
> >
> >  
> >
> > > yes, this is the issue. What you suggest should be fine and I am trying
> > > it now.
> > > With the locking version (and a fix to a bug I introduced) I got .0012%
> > > error
> > > on an overnight run with hpet layered on get_s_time_mono(), which is 
> > > the
> > > max(prev, cur) layer on get_s_time we discussed.
> > >   
> > 12 parts per million is pretty good. Is that cumulative deviation 
> > from 'wall
> > time' over ~12 hours?
> yes, deviation between the guest's time and an ntp reference.
>
> > That could easily be explained by the fact that Xen
> > system time is not sync'ed with ntp.
> >  
> That's true. And, as we have discussed, this error seems to vary quite 
> a bit
> platform to platform for some reason. I will verify that this still is 
> the case.
> -Dave
>
> > -- Keir
> >
> >
> >  

diff -r 483d006cc607 xen/arch/x86/time.c
--- a/xen/arch/x86/time.c       Fri Apr 25 13:46:27 2008 +0100
+++ b/xen/arch/x86/time.c       Fri Apr 25 15:40:31 2008 -0400
@@ -836,9 +836,9 @@ static void local_time_calibration(void 
 
     /* Disable IRQs to get 'instantaneous' current timestamps. */
     local_irq_disable();
+    curr_master_stime = read_platform_stime();
+    curr_local_stime  = get_s_time();
     rdtscll(curr_tsc);
-    curr_local_stime  = get_s_time();
-    curr_master_stime = read_platform_stime();
     local_irq_enable();
 
 #if 0

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