Re: [Xen-devel] [PATCHv9 3/4] gnttab: make the grant table lock a read-write lock

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 21.05.15 at 15:36, <david.vrabel@xxxxxxxxxx> wrote:
> On 21/05/15 11:32, Jan Beulich wrote:
>>>>> On 20.05.15 at 17:54, <david.vrabel@xxxxxxxxxx> wrote:
>>> @@ -827,9 +828,11 @@ __gnttab_map_grant_ref(
>>>              if ( (wrc + rdc) == 0 )
>>>                  err = iommu_map_page(ld, frame, frame, IOMMUF_readable);
>>>          }
>>> +
>>> +        double_gt_lock(lgt, rgt);
>> 
>> unlock. And with this code path actually used (due to the bug it's
>> pretty clear it didn't get exercised in your testing), how does
>> performance look like? 
> 
> I think it will be no worse than what it was before -- this path already
> really sucks (mapcount() loops over 1000s of entries).  I don't care
> about this path at all.

It's kind of strange that you don't care about this case - afaict we're
not getting there by default solely because dom0-strict mode is not
currently the default (albeit arguably it should be).

Jan


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