Re: [Xen-devel] [PATCH 0/9] qspinlock stuff -v15

[David Vrabel <david.vrabel@citrix.com>]

On 16/03/15 13:16, Peter Zijlstra wrote:
> Hi Waiman,
> 
> As promised; here is the paravirt stuff I did during the trip to BOS last week.
> 
> All the !paravirt patches are more or less the same as before (the only real
> change is the copyright lines in the first patch).
> 
> The paravirt stuff is 'simple' and KVM only -- the Xen code was a little more
> convoluted and I've no real way to test that but it should be stright fwd to
> make work.
> 
> I ran this using the virtme tool (thanks Andy) on my laptop with a 4x
> overcommit on vcpus (16 vcpus as compared to the 4 my laptop actually has) and
> it both booted and survived a hackbench run (perf bench sched messaging -g 20
> -l 5000).
> 
> So while the paravirt code isn't the most optimal code ever conceived it does work.
> 
> Also, the paravirt patching includes replacing the call with "movb $0, %arg1"
> for the native case, which should greatly reduce the cost of having
> CONFIG_PARAVIRT_SPINLOCKS enabled on actual hardware.
> 
> I feel that if someone were to do a Xen patch we can go ahead and merge this
> stuff (finally!).

I can look at this.  It looks pretty straight-forward.

> These patches do not implement the paravirt spinlock debug stats currently
> implemented (separately) by KVM and Xen, but that should not be too hard to do
> on top and in the 'generic' code -- no reason to duplicate all that.

I think this is fine.

David