Re: [Xen-users] clocksource/0: Time went backwards

[Bart Verwilst <lists@xxxxxxxxxxx>]

Well, i've found this link earlier: 
http://lists.xensource.com/archives/html/xen-devel/2006-03/msg00442.html , but 
it seems the code has changed quite a bit since then..
Big parts of the patch seem integrated already though.. 
For example:

Current patch, in use in my running kernel:

+       if ((blocked > 0) && (delta_cpu > 0)) {
+               delta_cpu -= blocked;
+               if (unlikely(delta_cpu < 0))
+                       blocked += delta_cpu; /* clamp local-time progress */
+               do_div(blocked, NS_PER_TICK);
+               per_cpu(processed_blocked_time, cpu) += blocked * NS_PER_TICK;
+               per_cpu(processed_system_time, cpu)  += blocked * NS_PER_TICK;


Patch on the link provided above:

        if (stolen > 0) {
                delta_cpu -= stolen;
+               if (unlikely(delta_cpu < 0)) {
+                       stolen += delta_cpu;
+                       delta_cpu = blocked = 0;
+               }
                do_div(stolen, NS_PER_TICK);
                per_cpu(processed_stolen_time, cpu) += stolen * NS_PER_TICK;
                per_cpu(processed_system_time, cpu) += stolen * NS_PER_TICK;

As you can see, quite different.. "delta_cpu = blocked = 0;" is missing, but 
might be handled with the rest of the changes in the new code..

Another possibility is that this only applies for i386 (i'm running on x86_64.. 
)..
I've looked into the patch, and it seems to only patch file 
arch/i386/kernel/time-xen.c .
There isn't a x86_64 equivalent.. ( arch/x86_64/kernel/time-xen.c doesn't exist 
) Is this normal? Could this be the cause?

Thanks a lot for your reply!

Kind regards,

Bart Verwilst

----- Original Message -----
From: "Shane D. Johnson" <SDJ@xxxxxxxxxxxxxxxxxxxxxx>
To: "Bart Verwilst" <lists@xxxxxxxxxxx>
Cc: Xen-users@xxxxxxxxxxxxxxxxxxx
Sent: Thursday, October 11, 2007 1:05:39 AM (GMT+0100) Europe/Berlin
Subject: Re: [Xen-users] clocksource/0: Time went backwards

Bart,
    I haven't had this happen but I  have seen a lot of references to 
similar problems on the mailing list archive.  I would start there and 
see if you can find your fix there.

Shane

Bart Verwilst wrote:
> Just happened again...
> Nobody has an idea what might be happening? This is obviously some kind of 
> bug.. :)
>
> Thanks!
>
> Bart
>
> ----- Original Message -----
> From: "Lists" <lists@xxxxxxxxxxx>
> To: Xen-users@xxxxxxxxxxxxxxxxxxx
> Sent: Wednesday, October 10, 2007 12:08:09 AM (GMT+0100) Europe/Berlin
> Subject: [Xen-users] clocksource/0: Time went backwards
>
> Dear fellow Xen'ers!
>
> I'm having a problem with my new Xen-enabled colocation server.. I hope ( at 
> least ;) ) one of you guys know how to fix this problem..
>
> For a certain amount of time ( 1-2 days ) the domU runs fine.. until the 
> console starts spitting out messages like these:
>
> [80182.004456] clocksource/0: Time went backwards: delta=-6917292717540055641 
> shadow=80182004054805 offset=400471
> [80182.004507] clocksource/0: Time went backwards: delta=-6917292717540005396 
> shadow=80182004054805 offset=450712
> [80182.004762] clocksource/0: Time went backwards: delta=-6917292717539750360 
> shadow=80182004054805 offset=705812
> [80182.004842] clocksource/0: Time went backwards: delta=-6917292717539670405 
> shadow=80182004054805 offset=785744
> [80182.004918] clocksource/0: Time went backwards: delta=-6917292717539594298 
> shadow=80182004054805 offset=861851
>
> The only action left is an xm shutdown, after which an xm create boots up the 
> machine fine for the next couple of days..
>
> I'm running Ubuntu 7.10, with the stock xen kernel ( 2.6.22-13-xen ).
>
> An ubuntu bug has already been reported and appended to by multiple persons 
> here:
>
> https://bugs.launchpad.net/ubuntu/+source/linux-source-2.6.22/+bug/146924
>
> Anyone have any ideas/patches/hints/.../anything that can help?
>
> Thanks a lot guys!
>
> Kind regards,
>
> Bart Verwilst
>
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>
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