[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCHv9 3/4] gnttab: make the grant table lock a read-write lock
On 22/05/15 07:37, Jan Beulich wrote: >>>> On 21.05.15 at 17:16, <david.vrabel@xxxxxxxxxx> wrote: >> On 21/05/15 15:53, Jan Beulich wrote: >>>>>> 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). >> >> What's your point? Are you going to refuse this series unless it also >> optimizes dom0-strict mode? > > No, I'm certainly not going to be. But this series of "I don't care" > worry me to a certain degree (apart from making me wonder > why, as so far I thought an as secure as possible environment is > key for XenServer, and "iommu=dom0-strict" is certainly helping > with that, which is also why I said that this should arguably > become the default). dom0-strict mode doesn't align with our PV-IOMMU plans to make BFN == PFN (including for grants). David _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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