RE: [Xen-devel] [PATCH][RFC] remove PV/x86 warnings (time went backwards)

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

"Time went backward" warnings are indicator that something goes
wrong. It's not a solution to remove the warning while leaving actual
reason unsolved.

Which release are you trying? Does it happen on up-to-date xen
unstable?

Thanks,
Kevin

>From: Atsushi SAKAI
>Sent: Thursday, December 11, 2008 4:03 PM
>
>Hi,
>
>This patch intends to remove warnings for Time went backwards
>(negative delta) like follows.
>========from Xen BZ 195
>Timer ISR/0: Time went backwards: delta=-10048465 cpu_delta=9951535
>shadow=706605145 0: 71640046095
>========
>
>Currently (static u64) processed_system_time@xxxxxxxxxx
> uses for calculating jiffies and wall_clock.
>and the processed_system_time saves maximum vcpu time value of 
>per_cpu(processed_system_time).
>
>At timer_interrupt@xxxxxxxxxx,
>they calculate "delta" compared to vcpu time(shadow).
>sometimes the value goes to negative.
>This is because vcpu time is varies.(scheduler etc.)
>
>This patch just removes the warnings of PV/x86,
>(Other way is loosen "delta" checking.(current checking is < -10msec)
> Or vcpu synchronization is needed.)
>
>This problem occurs on current linux-2.6.18-xen tree only.
>Not occured on pv_ops kernel.
>
>Of course, delta_cpu comparison keeps 
>since it is just compares per_cpu variable only.
>
>==for paravirt_ops ==
>For paravirt_ops, time.c is completely changed.
>http://git.kernel.org/?p=linux/kernel/git/jeremy/xen.git;a=blob
>;f=arch/x86/xen/time.c;h=c9f7cda48ed78ecbe1b421c540bbe2b7776814
>00;hb=HEAD
>
>See also
>2006/07(which uses delta)
>http://lists.xensource.com/archives/html/xen-devel/2006-07/msg0
>0567.html
>2007/03(which does not uses delta)
>http://lists.xensource.com/archives/html/xen-devel/2007-03/msg0
>0554.html
>
>
>== Related Bugzilla ==
>This patch related to following bugzilla.
>
>XenBugzilla:
>Many Timer ISR: Time went backwards logs
>http://bugzilla.xensource.com/bugzilla/show_bug.cgi?id=195
>
>RedHat Bugzilla:
>Many "Timer ISR: Time went backwards" after booting xen kernel
>https://bugzilla.redhat.com/show_bug.cgi?id=222973
>
>
>Signed-off-by: Atsushi SAKAI <sakaia@xxxxxxxxxxxxxx>
>
>Thanks
>Atsushi SAKAI
>
>
_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel