Re: [patch 0/2] x86,pat: Reduce contention on the memtype_lock -V4

[Robin Holt]

On Wed, Mar 24, 2010 at 03:16:14AM +0100, Andi Kleen wrote:
> holt@xxxxxxx writes:
> 
> > Tracking memtype on x86 uses a single global spin_lock for either reading
> > or changing the memory type.  This includes changes made to page flags
> > which is perfectly parallel.
> >
> > Part one of the patchset makes the page-based tracking use cmpxchg
> > without a need for a lock.
> >
> > Part two of the patchset converts the spin_lock into a read/write lock.
> 
> I'm curious: in what workloads did you see contention?
> 
> For any scalability patches it would be always good to have a description
> of the workload.

It was a job using xpmem (an out of tree kernel module) which uses
vm_insert_pfn to establish ptes.  The scalability issues were shown
in the first patch.  I do not have any test which shows a performance
difference  with the spin_lock to rw_lock conversion.

Robin
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