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

["Xu, Anthony" <anthony.xu@xxxxxxxxx>]

Isaku Yamahata wrote:
> 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.


So you can use read/write lock, multiple reader one writer.
Because write is very rare, it will not impact performance, but it makes code 
in mm.c clear and easy to modify.
I think that's why read/write lock exist.


Anthony

_______________________________________________
Xen-ia64-devel mailing list
Xen-ia64-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-ia64-devel