Re: [PATCH v1 08/14] xprtrdma: Acquire MRs in rpcrdma_register_external()

Sagi Grimberg
2015-05-07T10:31:07Z

On 5/4/2015 8:57 PM, Chuck Lever wrote:
> Acquiring 64 MRs in rpcrdma_buffer_get() while holding the buffer
> pool lock is expensive, and unnecessary because most modern adapters
> can transfer 100s of KBs of payload using just a single MR.
>
> Instead, acquire MRs one-at-a-time as chunks are registered, and
> return them to rb_mws immediately during deregistration.
>
> Note: commit 539431a437d2 ("xprtrdma: Don't invalidate FRMRs if
> registration fails") is reverted: There is now a valid case where
> registration can fail (with -ENOMEM) but the QP is still in RTS.
>
> Signed-off-by: Chuck Lever <chuck.lever-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>
> ---
> net/sunrpc/xprtrdma/frwr_ops.c | 120 ++++++++++++++++++++++++++++------------
> net/sunrpc/xprtrdma/rpc_rdma.c | 3 -
> net/sunrpc/xprtrdma/verbs.c | 21 -------
> 3 files changed, 86 insertions(+), 58 deletions(-)
>
> diff --git a/net/sunrpc/xprtrdma/frwr_ops.c b/net/sunrpc/xprtrdma/frwr_ops.c
> index a06d9a3..6f93a89 100644
> --- a/net/sunrpc/xprtrdma/frwr_ops.c
> +++ b/net/sunrpc/xprtrdma/frwr_ops.c
> @@ -11,6 +11,62 @@
> * but most complex memory registration mode.
> */
>
> +/* Normal operation
> + *
> + * A Memory Region is prepared for RDMA READ or WRITE using a FAST_REG
> + * Work Request (frmr_op_map). When the RDMA operation is finished, this
> + * Memory Region is invalidated using a LOCAL_INV Work Request
> + * (frmr_op_unmap).
> + *
> + * Typically these Work Requests are not signaled, and neither are RDMA
> + * SEND Work Requests (with the exception of signaling occasionally to
> + * prevent provider work queue overflows). This greatly reduces HCA
> + * interrupt workload.
> + *
> + * As an optimization, frwr_op_unmap marks MRs INVALID before the
> + * LOCAL_INV WR is posted. If posting succeeds, the MR is placed on
> + * rb_mws immediately so that no work (like managing a linked list
> + * under a spinlock) is needed in the completion upcall.
> + *
> + * But this means that frwr_op_map() can occasionally encounter an MR
> + * that is INVALID but the LOCAL_INV WR has not completed. Work Queue
> + * ordering prevents a subsequent FAST_REG WR from executing against
> + * that MR while it is still being invalidated.
> + */
> +
> +/* Transport recovery
> + *
> + * ->op_map and the transport connect worker cannot run at the same
> + * time, but ->op_unmap can fire while the transport connect worker
> + * is running. Thus MR recovery is handled in ->op_map, to guarantee
> + * that recovered MRs are owned by a sending RPC, and not one where
> + * ->op_unmap could fire at the same time transport reconnect is
> + * being done.
> + *
> + * When the underlying transport disconnects, MRs are left in one of
> + * three states:
> + *
> + * INVALID: The MR was not in use before the QP entered ERROR state.
> + * (Or, the LOCAL_INV WR has not completed or flushed yet).
> + *
> + * STALE: The MR was being registered or unregistered when the QP
> + * entered ERROR state, and the pending WR was flushed.
> + *
> + * VALID: The MR was registered before the QP entered ERROR state.
> + *
> + * When frwr_op_map encounters STALE and VALID MRs, they are recovered
> + * with ib_dereg_mr and then are re-initialized. Beause MR recovery
> + * allocates fresh resources, it is deferred to a workqueue, and the
> + * recovered MRs are placed back on the rb_mws list when recovery is
> + * complete. frwr_op_map allocates another MR for the current RPC while
> + * the broken MR is reset.
> + *
> + * To ensure that frwr_op_map doesn't encounter an MR that is marked
> + * INVALID but that is about to be flushed due to a previous transport
> + * disconnect, the transport connect worker attempts to drain all
> + * pending send queue WRs before the transport is reconnected.
> + */
> +
> #include "xprt_rdma.h"
>
> #if IS_ENABLED(CONFIG_SUNRPC_DEBUG)
> @@ -250,9 +306,9 @@ frwr_op_map(struct rpcrdma_xprt *r_xprt, struct rpcrdma_mr_seg *seg,
> struct ib_device *device = ia->ri_device;
> enum dma_data_direction direction = rpcrdma_data_dir(writing);
> struct rpcrdma_mr_seg *seg1 = seg;
> - struct rpcrdma_mw *mw = seg1->rl_mw;
> - struct rpcrdma_frmr *frmr = &mw->r.frmr;
> - struct ib_mr *mr = frmr->fr_mr;
> + struct rpcrdma_mw *mw;
> + struct rpcrdma_frmr *frmr;
> + struct ib_mr *mr;
> struct ib_send_wr fastreg_wr, *bad_wr;
> u8 key;
> int len, pageoff;
> @@ -261,12 +317,25 @@ frwr_op_map(struct rpcrdma_xprt *r_xprt, struct rpcrdma_mr_seg *seg,
> u64 pa;
> int page_no;
>
> + mw = seg1->rl_mw;
> + seg1->rl_mw = NULL;
> + do {
> + if (mw)
> + __frwr_queue_recovery(mw);
> + mw = rpcrdma_get_mw(r_xprt);
> + if (!mw)
> + return -ENOMEM;
> + } while (mw->r.frmr.fr_state != FRMR_IS_INVALID);
> + frmr = &mw->r.frmr;
> + frmr->fr_state = FRMR_IS_VALID;
> +
> pageoff = offset_in_page(seg1->mr_offset);
> seg1->mr_offset -= pageoff; /* start of page */
> seg1->mr_len += pageoff;
> len = -pageoff;
> if (nsegs > ia->ri_max_frmr_depth)
> nsegs = ia->ri_max_frmr_depth;
> +
> for (page_no = i = 0; i < nsegs;) {
> rpcrdma_map_one(device, seg, direction);
> pa = seg->mr_dma;
> @@ -285,8 +354,6 @@ frwr_op_map(struct rpcrdma_xprt *r_xprt, struct rpcrdma_mr_seg *seg,
> dprintk("RPC: %s: Using frmr %p to map %d segments (%d bytes)\n",
> __func__, mw, i, len);
>
> - frmr->fr_state = FRMR_IS_VALID;
> -
> memset(&fastreg_wr, 0, sizeof(fastreg_wr));
> fastreg_wr.wr_id = (unsigned long)(void *)mw;
> fastreg_wr.opcode = IB_WR_FAST_REG_MR;
> @@ -298,6 +365,7 @@ frwr_op_map(struct rpcrdma_xprt *r_xprt, struct rpcrdma_mr_seg *seg,
> fastreg_wr.wr.fast_reg.access_flags = writing ?
> IB_ACCESS_REMOTE_WRITE | IB_ACCESS_LOCAL_WRITE :
> IB_ACCESS_REMOTE_READ;
> + mr = frmr->fr_mr;
> key = (u8)(mr->rkey & 0x000000FF);
> ib_update_fast_reg_key(mr, ++key);
> fastreg_wr.wr.fast_reg.rkey = mr->rkey;
> @@ -307,6 +375,7 @@ frwr_op_map(struct rpcrdma_xprt *r_xprt, struct rpcrdma_mr_seg *seg,
> if (rc)
> goto out_senderr;
>
> + seg1->rl_mw = mw;
> seg1->mr_rkey = mr->rkey;
> seg1->mr_base = seg1->mr_dma + pageoff;
> seg1->mr_nsegs = i;
> @@ -315,10 +384,9 @@ frwr_op_map(struct rpcrdma_xprt *r_xprt, struct rpcrdma_mr_seg *seg,
>
> out_senderr:
> dprintk("RPC: %s: ib_post_send status %i\n", __func__, rc);
> - ib_update_fast_reg_key(mr, --key);
> - frmr->fr_state = FRMR_IS_INVALID;
> while (i--)
> rpcrdma_unmap_one(device, --seg);
> + __frwr_queue_recovery(mw);
> return rc;
> }
>
> @@ -330,15 +398,19 @@ frwr_op_unmap(struct rpcrdma_xprt *r_xprt, struct rpcrdma_mr_seg *seg)
> {
> struct rpcrdma_mr_seg *seg1 = seg;
> struct rpcrdma_ia *ia = &r_xprt->rx_ia;
> + struct rpcrdma_mw *mw = seg1->rl_mw;
> struct ib_send_wr invalidate_wr, *bad_wr;
> int rc, nsegs = seg->mr_nsegs;
>
> - seg1->rl_mw->r.frmr.fr_state = FRMR_IS_INVALID;
> + dprintk("RPC: %s: FRMR %p\n", __func__, mw);
> +
> + seg1->rl_mw = NULL;
> + mw->r.frmr.fr_state = FRMR_IS_INVALID;
>
> memset(&invalidate_wr, 0, sizeof(invalidate_wr));
> - invalidate_wr.wr_id = (unsigned long)(void *)seg1->rl_mw;
> + invalidate_wr.wr_id = (unsigned long)(void *)mw;
> invalidate_wr.opcode = IB_WR_LOCAL_INV;
> - invalidate_wr.ex.invalidate_rkey = seg1->rl_mw->r.frmr.fr_mr->rkey;
> + invalidate_wr.ex.invalidate_rkey = mw->r.frmr.fr_mr->rkey;
> DECR_CQCOUNT(&r_xprt->rx_ep);
>
> while (seg1->mr_nsegs--)
> @@ -348,12 +420,13 @@ frwr_op_unmap(struct rpcrdma_xprt *r_xprt, struct rpcrdma_mr_seg *seg)
> read_unlock(&ia->ri_qplock);
> if (rc)
> goto out_err;
> +
> + rpcrdma_put_mw(r_xprt, mw);
> return nsegs;
>
> out_err:
> - /* Force rpcrdma_buffer_get() to retry */
> - seg1->rl_mw->r.frmr.fr_state = FRMR_IS_STALE;
> dprintk("RPC: %s: ib_post_send status %i\n", __func__, rc);
> + __frwr_queue_recovery(mw);
> return nsegs;
> }
>
> @@ -370,29 +443,6 @@ out_err:
> static void
> frwr_op_reset(struct rpcrdma_xprt *r_xprt)
> {
> - struct rpcrdma_buffer *buf = &r_xprt->rx_buf;
> - struct ib_device *device = r_xprt->rx_ia.ri_device;
> - unsigned int depth = r_xprt->rx_ia.ri_max_frmr_depth;
> - struct ib_pd *pd = r_xprt->rx_ia.ri_pd;
> - struct rpcrdma_mw *r;
> - int rc;
> -
> - list_for_each_entry(r, &buf->rb_all, mw_all) {
> - if (r->r.frmr.fr_state == FRMR_IS_INVALID)
> - continue;
> -
> - __frwr_release(r);
> - rc = __frwr_init(r, pd, device, depth);
> - if (rc) {
> - dprintk("RPC: %s: mw %p left %s\n",
> - __func__, r,
> - (r->r.frmr.fr_state == FRMR_IS_STALE ?
> - "stale" : "valid"));
> - continue;
> - }
> -
> - r->r.frmr.fr_state = FRMR_IS_INVALID;
> - }
> }
>
> static void
> diff --git a/net/sunrpc/xprtrdma/rpc_rdma.c b/net/sunrpc/xprtrdma/rpc_rdma.c
> index 98a3b95..35ead0b 100644
> --- a/net/sunrpc/xprtrdma/rpc_rdma.c
> +++ b/net/sunrpc/xprtrdma/rpc_rdma.c
> @@ -284,9 +284,6 @@ rpcrdma_create_chunks(struct rpc_rqst *rqst, struct xdr_buf *target,
> return (unsigned char *)iptr - (unsigned char *)headerp;
>
> out:
> - if (r_xprt->rx_ia.ri_memreg_strategy == RPCRDMA_FRMR)
> - return n;
> -
> for (pos = 0; nchunks--;)
> pos += r_xprt->rx_ia.ri_ops->ro_unmap(r_xprt,
> &req->rl_segments[pos]);
> diff --git a/net/sunrpc/xprtrdma/verbs.c b/net/sunrpc/xprtrdma/verbs.c
> index 8a43c7ef..5226161 100644
> --- a/net/sunrpc/xprtrdma/verbs.c
> +++ b/net/sunrpc/xprtrdma/verbs.c
> @@ -1343,12 +1343,11 @@ rpcrdma_buffer_get_frmrs(struct rpcrdma_req *req, struct rpcrdma_buffer *buf,
> struct rpcrdma_req *
> rpcrdma_buffer_get(struct rpcrdma_buffer *buffers)
> {
> - struct rpcrdma_ia *ia = rdmab_to_ia(buffers);
> - struct list_head stale;
> struct rpcrdma_req *req;
> unsigned long flags;
>
> spin_lock_irqsave(&buffers->rb_lock, flags);
> +
> if (buffers->rb_send_index == buffers->rb_max_requests) {
> spin_unlock_irqrestore(&buffers->rb_lock, flags);
> dprintk("RPC: %s: out of request buffers\n", __func__);
> @@ -1367,17 +1366,7 @@ rpcrdma_buffer_get(struct rpcrdma_buffer *buffers)
> }
> buffers->rb_send_bufs[buffers->rb_send_index++] = NULL;
>
> - INIT_LIST_HEAD(&stale);
> - switch (ia->ri_memreg_strategy) {
> - case RPCRDMA_FRMR:
> - req = rpcrdma_buffer_get_frmrs(req, buffers, &stale);
> - break;
> - default:
> - break;
> - }
> spin_unlock_irqrestore(&buffers->rb_lock, flags);
> - if (!list_empty(&stale))
> - rpcrdma_retry_flushed_linv(&stale, buffers);
> return req;
> }
>
> @@ -1389,18 +1378,10 @@ void
> rpcrdma_buffer_put(struct rpcrdma_req *req)
> {
> struct rpcrdma_buffer *buffers = req->rl_buffer;
> - struct rpcrdma_ia *ia = rdmab_to_ia(buffers);
> unsigned long flags;
>
> spin_lock_irqsave(&buffers->rb_lock, flags);
> rpcrdma_buffer_put_sendbuf(req, buffers);
> - switch (ia->ri_memreg_strategy) {
> - case RPCRDMA_FRMR:
> - rpcrdma_buffer_put_mrs(req, buffers);
> - break;
> - default:
> - break;
> - }
> spin_unlock_irqrestore(&buffers->rb_lock, flags);
> }
>
>

Don't you need a call to flush_workqueue(frwr_recovery_wq) when you're
about to destroy the endpoint (and the buffers and the MRs...)?
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