Hi Anatoly, After using iova-mode=va, i see my ports are not getting detected ? I thought it's working but I see following problem
what could be the problem? i) I see allocation is faster ii) But my ports are not getting detected I take my word back that it entirely working.. Thanks, Regards, Venu On Thu, 14 Nov 2019 at 15:27, Burakov, Anatoly <anatoly.bura...@intel.com> wrote: > On 14-Nov-19 9:50 AM, Venumadhav Josyula wrote: > > Hi Anatoly, > > > > Thanks for quick response. We want to understand, if there will be > > performance implications because of iova-mode being va. We want to > > understand, specifically in terms following > > > > * cache misses > > * Branch misses etc > > * translation of va addr -> phy addr when packet is receieved > > > > There will be no impact whatsoever. You mentioned that you were already > using VFIO, so you were already making use of IOMMU*. Cache/branch > misses are independent of IOVA layout, and translations are done by the > hardware (in either IOVA as PA or IOVA as VA case - IOMMU doesn't care > what you program it with, it still does the translation, even if it's a > 1:1 IOVA-to-PA mapping), so there is nothing that can cause degradation. > > In fact, under some circumstances, using IOVA as VA mode can be used to > get performance /gains/, because the code can take advantage of the fact > that there are large IOVA-contiguous segments and no page-by-page > allocations. Some drivers (IIRC octeontx mempool?) even refuse to work > in IOVA as PA mode due to huge overheads of page-by-page buffer offset > tracking. > > TL;DR you'll be fine :) > > * Using an IOMMU can /theoretically/ affect performance due to hardware > IOVA->PA translation and IOTLB cache misses. In practice, i have never > been able to observe /any/ effect whatsoever on performance when using > IOMMU vs. without using IOMMU, so this appears to not be a concern /in > practice/. > > > Thanks and regards > > Venu > > > > On Thu, 14 Nov 2019 at 15:14, Burakov, Anatoly > > <anatoly.bura...@intel.com <mailto:anatoly.bura...@intel.com>> wrote: > > > > On 13-Nov-19 9:01 PM, Venumadhav Josyula wrote: > > > Hi Anatoly, > > > > > > By default w/o specifying --iova-mode option is iova-mode=pa by > > default ? > > > > > > Thanks > > > Venu > > > > > > > In 18.11, there is a very specific set of circumstances that will > > default to IOVA as VA mode. Future releases have become more > > aggressive, > > to the point of IOVA as VA mode being the default unless asked > > otherwise. So yes, it is highly likely that in your case, IOVA as PA > is > > picked as the default. > > > > -- > > Thanks, > > Anatoly > > > > > -- > Thanks, > Anatoly >
