Re: [Xen-devel] [timer/ticks related] dom0 hang during boot on large 1TB system

[Mukesh Rathor <mukesh.rathor@xxxxxxxxxx>]

On Fri, 18 Dec 2009 09:13:32 +0000
Keir Fraser <keir.fraser@xxxxxxxxxxxxx> wrote:

> On 18/12/2009 08:42, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:
> 
> >> This isn't really Xen time code, but unchanged Linux time code. I
> >> don't know which tree you quoted the code from -- 2.6.18 has
> >> similar but not identical. Anyway, I suggest try using the
> >> jiffy-comparison macros from <linux/jiffies.h>: time_before(),
> >> time_after(), etc. These are designed to work even when jiffies
> >> wraps. Feel free to send patch(es) for that, if you test that out
> >> and it works okay.
> > 
> > But regardless of that - shouldn't the page scrubbing really be a
> > background operation these days, and as such be (relatively)
> > performance neutral to the booting of Dom0?
> 
> We synchronously scrub free memory before starting dom0, and then
> subsequently scrub memory only for dying domains. So I don't know what
> scrubbing would be going on during dom0's boot-time calibrations, on
> any version of Xen, actually.
> 
>  -- Keir
> 

Scrubbing has nothing to do with the bug. It's just that the timing is just
right to expose the bug. The system boots fine with lesser memory. Since
hyp does:
       create dom0, page scrub, unpause dom0.

It appears with large scrubbing, this gets delta in dom0 timer_interrupt() 
to be large enough that jiffies wraps. 

Hope that makes sense.

thanks,
Mukesh


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