Re: [PATCH rdma-core 1/7] libhns: Fix calculation errors with ilog32()

[Jason Gunthorpe <jgg@ziepe.ca>]

On Fri, Nov 22, 2019 at 02:58:44AM +0000, Zengtao (B) wrote:
> > From: linux-rdma-owner@vger.kernel.org
> > [mailto:linux-rdma-owner@vger.kernel.org] On Behalf Of Weihang Li
> > Sent: Thursday, November 21, 2019 9:19 AM
> > To: jgg@ziepe.ca; leon@kernel.org
> > Cc: dledford@redhat.com; linux-rdma@vger.kernel.org; Linuxarm
> > Subject: [PATCH rdma-core 1/7] libhns: Fix calculation errors with ilog32()
> > 
> > Current calculation results using ilog32() is larger than expected, which
> > will lead to driver broken. The following is the log when QP creations
> > fails:
> > 
> > [   81.294844] hns3 0000:7d:00.0 hns_0: check SQ size error!
> > [   81.294848] hns3 0000:7d:00.0 hns_0: check SQ size error!
> > [   81.300225] hns3 0000:7d:00.0 hns_0: Sanity check sq size failed
> > [   81.300227] hns3 0000:7d:00.0: hns_roce_set_user_sq_size error for
> > create qp
> > [   81.305602] hns3 0000:7d:00.0 hns_0: Sanity check sq size failed
> > [   81.305603] hns3 0000:7d:00.0: hns_roce_set_user_sq_size error for
> > create qp
> > [   81.311589] hns3 0000:7d:00.0 hns_0: Create RC QP 0x000000
> > failed(-22)
> > [   81.318603] hns3 0000:7d:00.0 hns_0: Create RC QP 0x000000
> > failed(-22)
> > 
> > Fixes: b6cd213b276f ("libhns: Refactor for creating qp")
> > Signed-off-by: Weihang Li <liweihang@hisilicon.com>
> >  providers/hns/hns_roce_u_verbs.c | 11 ++++++-----
> >  1 file changed, 6 insertions(+), 5 deletions(-)
> > 
> > diff --git a/providers/hns/hns_roce_u_verbs.c
> > b/providers/hns/hns_roce_u_verbs.c
> > index 9d222c0..bd5060d 100644
> > +++ b/providers/hns/hns_roce_u_verbs.c
> > @@ -645,7 +645,8 @@ static int hns_roce_calc_qp_buff_size(struct
> > ibv_pd *pd, struct ibv_qp_cap *cap,
> >  	int page_size = to_hr_dev(pd->context->device)->page_size;
> > 
> >  	if (to_hr_dev(pd->context->device)->hw_version ==
> > HNS_ROCE_HW_VER1) {
> > -		qp->rq.wqe_shift = ilog32(sizeof(struct hns_roce_rc_rq_wqe));
> > +		qp->rq.wqe_shift =
> > +				ilog32(sizeof(struct hns_roce_rc_rq_wqe)) - 1;
> > 
> >  		qp->buf_size = align((qp->sq.wqe_cnt << qp->sq.wqe_shift),
> >  				     page_size) +
> > @@ -662,7 +663,7 @@ static int hns_roce_calc_qp_buff_size(struct
> > ibv_pd *pd, struct ibv_qp_cap *cap,
> >  	} else {
> >  		unsigned int rqwqe_size = HNS_ROCE_SGE_SIZE *
> > cap->max_recv_sge;
> > 
> > -		qp->rq.wqe_shift = ilog32(rqwqe_size);
> > +		qp->rq.wqe_shift = ilog32(rqwqe_size) - 1;
> > 
> >  		if (qp->sq.max_gs > HNS_ROCE_SGE_IN_WQE || type ==
> > IBV_QPT_UD)
> >  			qp->sge.sge_shift = HNS_ROCE_SGE_SHIFT;
> > @@ -747,8 +748,8 @@ static void hns_roce_set_qp_params(struct
> > ibv_pd *pd,
> >  		qp->rq.wqe_cnt =
> > roundup_pow_of_two(attr->cap.max_recv_wr);
> >  	}
> > 
> > -	qp->sq.wqe_shift = ilog32(sizeof(struct hns_roce_rc_send_wqe));
> > -	qp->sq.shift = ilog32(qp->sq.wqe_cnt);
> > +	qp->sq.wqe_shift = ilog32(sizeof(struct hns_roce_rc_send_wqe)) - 1;
> > +	qp->sq.shift = ilog32(qp->sq.wqe_cnt) - 1;
> 
> One suggestion, it's better to introduce a new micro instead of ilog32(x) -1.

Is the -1 even correct?

I would have guessed something called shift wants to be:

   shift = ilog32(qp->sq.wqe_cnt - 1)

Such that 
   1 << shift == wqe_cnt
       When wqe_cnt is a power of two.
   1 << shift > wqe_cnt
       When wqe_cnt is not a power of two.

Jason