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

[Mauro <mrsanna1@gmail.com>]

On 18 October 2012 10:33, Ian Campbell <Ian.Campbell@citrix.com> wrote:
> On Thu, 2012-10-18 at 08:55 +0100, Keir Fraser wrote:
>> On 18/10/2012 08:40, "Ian Campbell" <Ian.Campbell@citrix.com> 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.