On Wed, Sep 10, 2014 at 11:18 PM, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote: > Il 07/09/2014 12:32, Ming Lei ha scritto: >> It is a good idea to disable SG merge for vq incapable of indirect because >> there are very limited direct descriptors. > > I think you mean _enabling_ SG merge if indirect descriptors are not there. You are right, sorry for the typo. >> For vq capable of indirect, it should be better to not do SG merge at default >> because: >> >> - from hypervisor view, no matter how many segments one req has, all are >> submitted to host kernel by one syscall, such as readv/io_submit >> >> - host kernel still need to do the same merge again > > Here we agree. > > Paolo > >> From my test(virtio-blk over null_blk), looks enabling SG merge may cause >> throughput a little drop(~3%). > Thanks, -- Ming Lei _______________________________________________ Virtualization mailing list Virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx https://lists.linuxfoundation.org/mailman/listinfo/virtualization
