IB/mlx4: Use multiple WQ blocks to post smaller send WQEs

ConnectX HCA supports shrinking WQEs, so that a single work request
can be made of multiple units of wqe_shift.  This way, WRs can differ
in size, and do not have to be a power of 2 in size, saving memory and
speeding up send WR posting.  Unfortunately, if we do this then the
wqe_index field in CQEs can't be used to look up the WR ID anymore, so
our implementation does this only if selective signaling is off.

Further, on 32-bit platforms, we can't use vmap() to make the QP
buffer virtually contigious. Thus we have to use constant-sized WRs to
make sure a WR is always fully within a single page-sized chunk.

Finally, we use WRs with the NOP opcode to avoid wrapping around the
queue buffer in the middle of posting a WR, and we set the
NoErrorCompletion bit to avoid getting completions with error for NOP
WRs.  However, NEC is only supported starting with firmware 2.2.232,
so we use constant-sized WRs for older firmware.  And, since MLX QPs
only support SEND, we use constant-sized WRs in this case.

When stamping during NOP posting, do stamping following setting of the
NOP WQE valid bit.

Signed-off-by: Michael S. Tsirkin <mst@dev.mellanox.co.il>
Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Roland Dreier <rolandd@cisco.com>

1 files changed, 176 insertions, 34 deletions

diff --git a/drivers/infiniband/hw/mlx4/qp.c b/drivers/infiniband/hw/mlx4/qp.c
index 376db730bc75..958e205b6d7c 100644
--- a/drivers/infiniband/hw/mlx4/qp.c
+++ b/drivers/infiniband/hw/mlx4/qp.c
@@ -30,6 +30,8 @@
  * SOFTWARE.
  */
 
+#include <linux/log2.h>
+
 #include <rdma/ib_cache.h>
 #include <rdma/ib_pack.h>
 
@@ -111,16 +113,87 @@ static void *get_send_wqe(struct mlx4_ib_qp *qp, int n)
 
 /*
  * Stamp a SQ WQE so that it is invalid if prefetched by marking the
- * first four bytes of every 64 byte chunk with 0xffffffff, except for
- * the very first chunk of the WQE.
+ * first four bytes of every 64 byte chunk with
+ *     0x7FFFFFF | (invalid_ownership_value << 31).
+ *
+ * When the max work request size is less than or equal to the WQE
+ * basic block size, as an optimization, we can stamp all WQEs with
+ * 0xffffffff, and skip the very first chunk of each WQE.
  */
-static void stamp_send_wqe(struct mlx4_ib_qp *qp, int n)
+static void stamp_send_wqe(struct mlx4_ib_qp *qp, int n, int size)
 {
-        u32 *wqe = get_send_wqe(qp, n);
+        u32 *wqe;
         int i;
+        int s;
+        int ind;
+        void *buf;
+        __be32 stamp;
+
+        s = roundup(size, 1U << qp->sq.wqe_shift);
+        if (qp->sq_max_wqes_per_wr > 1) {
+                for (i = 0; i < s; i += 64) {
+                        ind = (i >> qp->sq.wqe_shift) + n;
+                        stamp = ind & qp->sq.wqe_cnt ? cpu_to_be32(0x7fffffff) :
+                                                       cpu_to_be32(0xffffffff);
+                        buf = get_send_wqe(qp, ind & (qp->sq.wqe_cnt - 1));
+                        wqe = buf + (i & ((1 << qp->sq.wqe_shift) - 1));
+                        *wqe = stamp;
+                }
+        } else {
+                buf = get_send_wqe(qp, n & (qp->sq.wqe_cnt - 1));
+                for (i = 64; i < s; i += 64) {
+                        wqe = buf + i;
+                        *wqe = 0xffffffff;
+                }
+        }
+}
+
+static void post_nop_wqe(struct mlx4_ib_qp *qp, int n, int size)
+{
+        struct mlx4_wqe_ctrl_seg *ctrl;
+        struct mlx4_wqe_inline_seg *inl;
+        void *wqe;
+        int s;
+
+        ctrl = wqe = get_send_wqe(qp, n & (qp->sq.wqe_cnt - 1));
+        s = sizeof(struct mlx4_wqe_ctrl_seg);
+
+        if (qp->ibqp.qp_type == IB_QPT_UD) {
+                struct mlx4_wqe_datagram_seg *dgram = wqe + sizeof *ctrl;
+                struct mlx4_av *av = (struct mlx4_av *)dgram->av;
+                memset(dgram, 0, sizeof *dgram);
+                av->port_pd = cpu_to_be32((qp->port << 24) | to_mpd(qp->ibqp.pd)->pdn);
+                s += sizeof(struct mlx4_wqe_datagram_seg);
+        }
+
+        /* Pad the remainder of the WQE with an inline data segment. */
+        if (size > s) {
+                inl = wqe + s;
+                inl->byte_count = cpu_to_be32(1 << 31 | (size - s - sizeof *inl));
+        }
+        ctrl->srcrb_flags = 0;
+        ctrl->fence_size = size / 16;
+        /*
+         * Make sure descriptor is fully written before setting ownership bit
+         * (because HW can start executing as soon as we do).
+         */
+        wmb();
+
+        ctrl->owner_opcode = cpu_to_be32(MLX4_OPCODE_NOP | MLX4_WQE_CTRL_NEC) |
+                (n & qp->sq.wqe_cnt ? cpu_to_be32(1 << 31) : 0);
 
-        for (i = 16; i < 1 << (qp->sq.wqe_shift - 2); i += 16)
-                wqe[i] = 0xffffffff;
+        stamp_send_wqe(qp, n + qp->sq_spare_wqes, size);
+}
+
+/* Post NOP WQE to prevent wrap-around in the middle of WR */
+static inline unsigned pad_wraparound(struct mlx4_ib_qp *qp, int ind)
+{
+        unsigned s = qp->sq.wqe_cnt - (ind & (qp->sq.wqe_cnt - 1));
+        if (unlikely(s < qp->sq_max_wqes_per_wr)) {
+                post_nop_wqe(qp, ind, s << qp->sq.wqe_shift);
+                ind += s;
+        }
+        return ind;
 }
 
 static void mlx4_ib_qp_event(struct mlx4_qp *qp, enum mlx4_event type)
@@ -237,6 +310,8 @@ static int set_rq_size(struct mlx4_ib_dev *dev, struct ib_qp_cap *cap,
 static int set_kernel_sq_size(struct mlx4_ib_dev *dev, struct ib_qp_cap *cap,
                               enum ib_qp_type type, struct mlx4_ib_qp *qp)
 {
+        int s;
+
         /* Sanity check SQ size before proceeding */
         if (cap->max_send_wr     > dev->dev->caps.max_wqes  ||
             cap->max_send_sge    > dev->dev->caps.max_sq_sg ||
@@ -252,20 +327,74 @@ static int set_kernel_sq_size(struct mlx4_ib_dev *dev, struct ib_qp_cap *cap,
             cap->max_send_sge + 2 > dev->dev->caps.max_sq_sg)
                 return -EINVAL;
 
-        qp->sq.wqe_shift = ilog2(roundup_pow_of_two(max(cap->max_send_sge *
-                                                        sizeof (struct mlx4_wqe_data_seg),
-                                                        cap->max_inline_data +
-                                                        sizeof (struct mlx4_wqe_inline_seg)) +
-                                                    send_wqe_overhead(type)));
-        qp->sq.max_gs    = ((1 << qp->sq.wqe_shift) - send_wqe_overhead(type)) /
-                sizeof (struct mlx4_wqe_data_seg);
+        s = max(cap->max_send_sge * sizeof (struct mlx4_wqe_data_seg),
+                cap->max_inline_data + sizeof (struct mlx4_wqe_inline_seg)) +
+                send_wqe_overhead(type);
 
         /*
-         * We need to leave 2 KB + 1 WQE of headroom in the SQ to
-         * allow HW to prefetch.
+         * Hermon supports shrinking WQEs, such that a single work
+         * request can include multiple units of 1 << wqe_shift.  This
+         * way, work requests can differ in size, and do not have to
+         * be a power of 2 in size, saving memory and speeding up send
+         * WR posting.  Unfortunately, if we do this then the
+         * wqe_index field in CQEs can't be used to look up the WR ID
+         * anymore, so we do this only if selective signaling is off.
+         *
+         * Further, on 32-bit platforms, we can't use vmap() to make
+         * the QP buffer virtually contigious.  Thus we have to use
+         * constant-sized WRs to make sure a WR is always fully within
+         * a single page-sized chunk.
+         *
+         * Finally, we use NOP work requests to pad the end of the
+         * work queue, to avoid wrap-around in the middle of WR.  We
+         * set NEC bit to avoid getting completions with error for
+         * these NOP WRs, but since NEC is only supported starting
+         * with firmware 2.2.232, we use constant-sized WRs for older
+         * firmware.
+         *
+         * And, since MLX QPs only support SEND, we use constant-sized
+         * WRs in this case.
+         *
+         * We look for the smallest value of wqe_shift such that the
+         * resulting number of wqes does not exceed device
+         * capabilities.
+         *
+         * We set WQE size to at least 64 bytes, this way stamping
+         * invalidates each WQE.
          */
-        qp->sq_spare_wqes = (2048 >> qp->sq.wqe_shift) + 1;
-        qp->sq.wqe_cnt = roundup_pow_of_two(cap->max_send_wr + qp->sq_spare_wqes);
+        if (dev->dev->caps.fw_ver >= MLX4_FW_VER_WQE_CTRL_NEC &&
+            qp->sq_signal_bits && BITS_PER_LONG == 64 &&
+            type != IB_QPT_SMI && type != IB_QPT_GSI)
+                qp->sq.wqe_shift = ilog2(64);
+        else
+                qp->sq.wqe_shift = ilog2(roundup_pow_of_two(s));
+
+        for (;;) {
+                if (1 << qp->sq.wqe_shift > dev->dev->caps.max_sq_desc_sz)
+                        return -EINVAL;
+
+                qp->sq_max_wqes_per_wr = DIV_ROUND_UP(s, 1U << qp->sq.wqe_shift);
+
+                /*
+                 * We need to leave 2 KB + 1 WR of headroom in the SQ to
+                 * allow HW to prefetch.
+                 */
+                qp->sq_spare_wqes = (2048 >> qp->sq.wqe_shift) + qp->sq_max_wqes_per_wr;
+                qp->sq.wqe_cnt = roundup_pow_of_two(cap->max_send_wr *
+                                                    qp->sq_max_wqes_per_wr +
+                                                    qp->sq_spare_wqes);
+
+                if (qp->sq.wqe_cnt <= dev->dev->caps.max_wqes)
+                        break;
+
+                if (qp->sq_max_wqes_per_wr <= 1)
+                        return -EINVAL;
+
+                ++qp->sq.wqe_shift;
+        }
+
+        qp->sq.max_gs = ((qp->sq_max_wqes_per_wr << qp->sq.wqe_shift) -
+                         send_wqe_overhead(type)) / sizeof (struct mlx4_wqe_data_seg);
 
         qp->buf_size = (qp->rq.wqe_cnt << qp->rq.wqe_shift) +
                 (qp->sq.wqe_cnt << qp->sq.wqe_shift);
@@ -277,7 +406,8 @@ static int set_kernel_sq_size(struct mlx4_ib_dev *dev, struct ib_qp_cap *cap,
                 qp->sq.offset = 0;
         }
 
-        cap->max_send_wr  = qp->sq.max_post = qp->sq.wqe_cnt - qp->sq_spare_wqes;
+        cap->max_send_wr  = qp->sq.max_post =
+                (qp->sq.wqe_cnt - qp->sq_spare_wqes) / qp->sq_max_wqes_per_wr;
         cap->max_send_sge = qp->sq.max_gs;
         /* We don't support inline sends for kernel QPs (yet) */
         cap->max_inline_data = 0;
@@ -323,6 +453,12 @@ static int create_qp_common(struct mlx4_ib_dev *dev, struct ib_pd *pd,
         qp->rq.tail         = 0;
         qp->sq.head         = 0;
         qp->sq.tail         = 0;
+        qp->sq_next_wqe     = 0;
+
+        if (init_attr->sq_sig_type == IB_SIGNAL_ALL_WR)
+                qp->sq_signal_bits = cpu_to_be32(MLX4_WQE_CTRL_CQ_UPDATE);
+        else
+                qp->sq_signal_bits = 0;
 
         err = set_rq_size(dev, &init_attr->cap, !!pd->uobject, !!init_attr->srq, qp);
         if (err)
@@ -413,11 +549,6 @@ static int create_qp_common(struct mlx4_ib_dev *dev, struct ib_pd *pd,
          */
         qp->doorbell_qpn = swab32(qp->mqp.qpn << 8);
 
-        if (init_attr->sq_sig_type == IB_SIGNAL_ALL_WR)
-                qp->sq_signal_bits = cpu_to_be32(MLX4_WQE_CTRL_CQ_UPDATE);
-        else
-                qp->sq_signal_bits = 0;
-
         qp->mqp.event = mlx4_ib_qp_event;
 
         return 0;
@@ -912,7 +1043,7 @@ static int __mlx4_ib_modify_qp(struct ib_qp *ibqp,
                         ctrl = get_send_wqe(qp, i);
                         ctrl->owner_opcode = cpu_to_be32(1 << 31);
 
-                        stamp_send_wqe(qp, i);
+                        stamp_send_wqe(qp, i, 1 << qp->sq.wqe_shift);
                 }
         }
 
@@ -965,6 +1096,7 @@ static int __mlx4_ib_modify_qp(struct ib_qp *ibqp,
                 qp->rq.tail = 0;
                 qp->sq.head = 0;
                 qp->sq.tail = 0;
+                qp->sq_next_wqe = 0;
                 if (!ibqp->srq)
                         *qp->db.db  = 0;
         }
@@ -1274,13 +1406,14 @@ int mlx4_ib_post_send(struct ib_qp *ibqp, struct ib_send_wr *wr,
         unsigned long flags;
         int nreq;
         int err = 0;
-        int ind;
-        int size;
+        unsigned ind;
+        int uninitialized_var(stamp);
+        int uninitialized_var(size);
         int i;
 
         spin_lock_irqsave(&qp->sq.lock, flags);
 
-        ind = qp->sq.head;
+        ind = qp->sq_next_wqe;
 
         for (nreq = 0; wr; ++nreq, wr = wr->next) {
                 if (mlx4_wq_overflow(&qp->sq, nreq, qp->ibqp.send_cq)) {
@@ -1296,7 +1429,7 @@ int mlx4_ib_post_send(struct ib_qp *ibqp, struct ib_send_wr *wr,
                 }
 
                 ctrl = wqe = get_send_wqe(qp, ind & (qp->sq.wqe_cnt - 1));
-                qp->sq.wrid[ind & (qp->sq.wqe_cnt - 1)] = wr->wr_id;
+                qp->sq.wrid[(qp->sq.head + nreq) & (qp->sq.wqe_cnt - 1)] = wr->wr_id;
 
                 ctrl->srcrb_flags =
                         (wr->send_flags & IB_SEND_SIGNALED ?
@@ -1409,16 +1542,23 @@ int mlx4_ib_post_send(struct ib_qp *ibqp, struct ib_send_wr *wr,
                 ctrl->owner_opcode = mlx4_ib_opcode[wr->opcode] |
                         (ind & qp->sq.wqe_cnt ? cpu_to_be32(1 << 31) : 0);
 
+                stamp = ind + qp->sq_spare_wqes;
+                ind += DIV_ROUND_UP(size * 16, 1U << qp->sq.wqe_shift);
+
                 /*
                  * We can improve latency by not stamping the last
                  * send queue WQE until after ringing the doorbell, so
                  * only stamp here if there are still more WQEs to post.
+                 *
+                 * Same optimization applies to padding with NOP wqe
+                 * in case of WQE shrinking (used to prevent wrap-around
+                 * in the middle of WR).
                  */
-                if (wr->next)
-                        stamp_send_wqe(qp, (ind + qp->sq_spare_wqes) &
-                                       (qp->sq.wqe_cnt - 1));
+                if (wr->next) {
+                        stamp_send_wqe(qp, stamp, size * 16);
+                        ind = pad_wraparound(qp, ind);
+                }
 
-                ++ind;
         }
 
 out:
@@ -1440,8 +1580,10 @@ out:
                  */
                 mmiowb();
 
-                stamp_send_wqe(qp, (ind + qp->sq_spare_wqes - 1) &
-                               (qp->sq.wqe_cnt - 1));
+                stamp_send_wqe(qp, stamp, size * 16);
+
+                ind = pad_wraparound(qp, ind);
+                qp->sq_next_wqe = ind;
         }
 
         spin_unlock_irqrestore(&qp->sq.lock, flags);