Re: [PATCH for-next 4/6] RDMA/hns: Filter for zero length of sge in hip08 kernel mode

[Leon Romanovsky <leon-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

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On Mon, Dec 25, 2017 at 06:08:08PM +0800, oulijun wrote:
> 在 2017/12/25 17:00, Leon Romanovsky 写道:
> > On Sat, Dec 23, 2017 at 04:22:20PM +0800, Lijun Ou wrote:
> >> When the length of sge is zero, the driver need to filter it
> >>
> >> Signed-off-by: Lijun Ou <oulijun-hv44wF8Li93QT0dZR+AlfA@public.gmane.org>
> >> ---
> >>  drivers/infiniband/hw/hns/hns_roce_hw_v2.c | 29 ++++++++++++++++++++---------
> >>  1 file changed, 20 insertions(+), 9 deletions(-)
> >>
> >> diff --git a/drivers/infiniband/hw/hns/hns_roce_hw_v2.c b/drivers/infiniband/hw/hns/hns_roce_hw_v2.c
> >> index 869e36f..a1d8ca0 100644
> >> --- a/drivers/infiniband/hw/hns/hns_roce_hw_v2.c
> >> +++ b/drivers/infiniband/hw/hns/hns_roce_hw_v2.c
> >> @@ -230,26 +230,37 @@ static int hns_roce_v2_post_send(struct ib_qp *ibqp, struct ib_send_wr *wr,
> >>  				     V2_RC_SEND_WQE_BYTE_4_INLINE_S, 1);
> >>  		} else {
> >>  			if (wr->num_sge <= 2) {
> >> -				for (i = 0; i < wr->num_sge; i++)
> >> -					set_data_seg_v2(dseg + i,
> >> -							wr->sg_list + i);
> >> +				for (i = 0; i < wr->num_sge; i++) {
> >> +					if (likely(wr->sg_list[i].length)) {
> >> +						set_data_seg_v2(dseg,
> >> +							       wr->sg_list + i);
> >> +						dseg++;
> >
> > Actually, you don't need to advance desg and keep your "desg + i" code as before.
> >
> > I have a more general question, is this scenario (having length == 0) real?
> >
> > Thanks
> >
> Yes, The origin plan for processing the length of sge is zero is that the hardware recognizes
> and filter it. but the final plan is that the software filter it and have an improved performance.
>

My question was an attempt to understand if kernel can create sg_list with length equal to zero.

Thanks

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