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

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2012-10-18 at 09:56 +0100, Mauro wrote:
> On 18 October 2012 10:33, Ian Campbell <Ian.Campbell@xxxxxxxxxx> wrote:
> > 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.
> 
> If that patch works debian kernel maintainers can be advised if they
> can include that patch and release a new kernel working for squeeze.

AFAIK this is a debug patch, not something we would deploy as is but it
should give us the information required to work out a real fix.

Ian


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