Re: [Xen-ia64-devel][PATCH][VTD] small patches for VTD

[Isaku Yamahata <yamahata@xxxxxxxxxxxxx>]

On Wed, Oct 22, 2008 at 02:11:52PM +0800, Xu, Anthony wrote:
> Isaku Yamahata wrote:
> > On Wed, Oct 22, 2008 at 01:56:05PM +0800, Xu, Anthony wrote:
> >> Yes, it is not SMP-safe there is lock for p2m.
> >> Modifying p2m is not a frequent operation, why not add a lock for it?
> >
> > It is frequent to read p2m table. So lockless approach was adopted
> > for scalability.
> > It doesn't make sense to lock around only writer side.
> >
> 
> If only add write lock for p2m, is there any bad impact/senario?
> Can you explain more details?

Generally lock should protect both readers and writers.
So locking around only writers doesn't make sense.
-- 
yamahata

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