Re: [Xen-devel] [Xen-users] Re: Xen 4 TSC problems

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2012-10-18 at 08:55 +0100, Keir Fraser wrote:
> On 18/10/2012 08:40, "Ian Campbell" <Ian.Campbell@xxxxxxxxxx> wrote:
> 
> > On Wed, 2012-10-17 at 17:15 +0100, Keir Fraser wrote:
> >> @@ -540,6 +541,14 @@ static void plt_overflow(void *unused)
> >>          plt_wrap = __read_platform_stime(plt_stamp64 + plt_mask + 1);
> >>          if ( ABS(plt_wrap - now) > ABS(plt_now - now) )
> >>              break;
> >> +        rdtscll(tsc);
> >> +        printk("XXX plt_overflow: plt_now=%"PRIx64" plt_wrap=%"PRIx64
> >> +               " now=%"PRIx64" old_stamp=%"PRIx64" new_stamp=%"PRIx64
> >> +               " plt_stamp64=%"PRIx64" plt_mask=%"PRIx64
> >> +               " tsc=%"PRIx64" tsc_stamp=%"PRIx64"\n",
> >> +               plt_now, plt_wrap, now, old_stamp, plt_stamp, plt_stamp64,
> >> +               plt_mask, tsc, this_cpu(cpu_time).local_tsc_stamp);
> >> +        break;
> > 
> > Is the break here, making the following update to plt_stamp64 dead code
> > deliberate?
> 
> Yes, it's a hack to disable the timer-has-apparently-wrapped workaround.

OK, good.

I wonder if this explains some of the issues which have been plaguing
Debian Squeeze (4.0 based) for a while now. I'll see if I can get
someone there to give it a go.

Ian.

> 
>  -- Keir
> 
> >>          plt_stamp64 += plt_mask + 1;
> >>      }
> >>      if ( i != 0 )
> > 
> > Ian.
> > 
> > 
> 
> 



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