Re: [Xen-devel] [PATCH v5 0/8] Memory scrubbing from idle loop

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 06/23/2017 09:22 AM, Jan Beulich wrote:
> > > > On 23.06.17 at 15:11, <boris.ostrovsky@xxxxxxxxxx> wrote:
> > On 06/23/2017 05:36 AM, Jan Beulich wrote:
> > > > > > On 22.06.17 at 20:57, <boris.ostrovsky@xxxxxxxxxx> wrote:
> > > > Deferred:
> > > > * Per-node heap locks. In addition to (presumably) improving performance in
> > > >     general, once they are available we can parallelize scrubbing further by
> > > >     allowing more than one core per node to do idle loop scrubbing.
> > > I don't understand: A per-node lock still calls for just one CPU
> > > doing the scrubbing on that node, in order to not congest the
> > > lock.
> >
> > Is this necessarily true? Maybe not allow all cores on a node to scrub
> > but I'd think having more than one core do the work may be beneficial.
> > Don't forget that actual scrubbing is performed without holding locks.
> > We only grab the lock to find dirty buddies in the heap.
> Hmm, true, but then I still don't see the connection between
> breaking up the lock and parallelizing scrubbing.
With a single heap lock we might indeed start seeing lock contention 
when multiple CPUs from many nodes are scrubbing. Making it per-node 
should lessen the pressure.
-boris

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