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SubjectRe: Preemptable Ticket Spinlock
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On Mon, 2013-04-22 at 15:56 -0400, Rik van Riel wrote:
> On 04/22/2013 03:49 PM, Peter Zijlstra wrote:
> > On Mon, 2013-04-22 at 08:52 -0400, Rik van Riel wrote:
>
> >> If the native spin_lock code has been called already at
> >> that time, the native code would still need to be modified
> >> to increment the ticket number by 2, so we end up with a
> >> compatible value in each spin lock's .tickets field, and
> >> prevent a deadlock after we switch over to the paravirt
> >> variant.
> >
> > I thought the stuff already made it upstream, but apparently not; the
> > lastest posting I'm aware of is here:
> >
> > https://lkml.org/lkml/2012/5/2/105
> >
> > That stuff changes the normal ticket increment as well..
>
> Jiannan,
>
> It looks like the patch above could make a good patch
> 1 (or 2) in your patch series :)

I much prefer the entire series from Jeremy since it maintains the
ticket semantics and doesn't degrade the lock to unfair under
contention.

Now I suppose there's a reason its not been merged yet and I suspect
its !paravirt hotpath impact which wasn't rightly justified or somesuch
so maybe someone can work on that or so.. dunno.




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