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SubjectRe: [PATCH] seqlock: serialize against writers

On Fri, 29 Aug 2008, Gregory Haskins wrote:

> Andi Kleen wrote:
> >> Im running it on a x86_64 box as we speak. How can I tell if there is a
> >> certain mode that is permitting this?
> >>
> >
> > If the boot up says you're running with PMtimer then it uses the fallback
> > (usually happens on pre Fam10h AMD boxes). A typical Intel box
> > would use the faster ring 3 only TSC path and then explode with your
> > change I bet.
> >
> > Or step with gdb through gettimeofday() and see if it does a syscall.
> >
> > -Andi
> >
> It seems to be running fine with no indication it has fallen back.
> Perhaps I need a certain workload to bring out the issue?

Perhaps you never hit the slow path in userland. That's the only place it
would write. Perhaps add a dummy static variable in the fast path, and
write to it. See if that crashes you apps.

-- Steve

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