Messages in this thread | | | Date | Wed, 10 Sep 2014 23:21:20 +0800 | Subject | Re: [PATCH] virtio_blk: merge S/G list entries by default | From | Ming Lei <> |
| |
On Wed, Sep 10, 2014 at 11:18 PM, Paolo Bonzini <pbonzini@redhat.com> 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
| |