On Mon, Aug 06, 2018 at 02:32:28PM +0530, Anshuman Khandual wrote: > On 08/05/2018 05:54 AM, Michael S. Tsirkin wrote: > > On Fri, Aug 03, 2018 at 08:21:26PM -0500, Benjamin Herrenschmidt wrote: > >> On Fri, 2018-08-03 at 22:08 +0300, Michael S. Tsirkin wrote: > >>>>>> Please go through these patches and review whether this approach broadly > >>>>>> makes sense. I will appreciate suggestions, inputs, comments regarding > >>>>>> the patches or the approach in general. Thank you. > >>>>> > >>>>> Jason did some work on profiling this. Unfortunately he reports > >>>>> about 4% extra overhead from this switch on x86 with no vIOMMU. > >>>> > >>>> The test is rather simple, just run pktgen (pktgen_sample01_simple.sh) in > >>>> guest and measure PPS on tap on host. > >>>> > >>>> Thanks > >>> > >>> Could you supply host configuration involved please? > >> > >> I wonder how much of that could be caused by Spectre mitigations > >> blowing up indirect function calls... > >> > >> Cheers, > >> Ben. > > > > I won't be surprised. If yes I suggested a way to mitigate the overhead. > > Did we get better results (lower regression due to indirect calls) with > the suggested mitigation ? Just curious. I'm referring to this: I wonder whether we can support map_sg and friends being NULL, then use that when mapping is an identity. A conditional branch there is likely very cheap. I don't think anyone tried implementing this yes. -- MST _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
