> On May 9, 2018, at 5:18 PM, J. Bruce Fields <bfields@xxxxxxxxxxxx> wrote:
>
> On Mon, May 07, 2018 at 03:27:43PM -0400, Chuck Lever wrote:
>> The current Receive path uses an array of pages which are allocated
>> and DMA mapped when each Receive WR is posted, and then handed off
>> to the upper layer in rqstp::rq_arg. The page flip releases unused
>> pages in the rq_pages pagelist. This mechanism introduces a
>> significant amount of overhead.
>>
>> So instead, kmalloc the Receive buffer, and leave it DMA-mapped
>> while the transport remains connected. This confers a number of
>> benefits:
>>
>> * Each Receive WR requires only one receive SGE, no matter how large
>> the inline threshold is. This helps the server-side NFS/RDMA
>> transport operate on less capable RDMA devices.
>>
>> * The Receive buffer is left allocated and mapped all the time. This
>> relieves svc_rdma_post_recv from the overhead of allocating and
>> DMA-mapping a fresh buffer.
>
> Dumb question: does that mean the buffer could still change if the
> client does something weird? (So could the xdr decoding code see data
> change out from under it?)
No, once the Receive completes, the HCA no longer has access
to the buffer. Leaving it DMA-mapped is not the same as leaving
it posted or leaving it registered; it just means that the I/O
subsystem has the buffer prepared for more I/O.
The current scheme works like this:
repeat:
Allocate a page
DMA-map the page
Post a Recv WR for that page
Recv WR completes
DMA-unmap the page
XDR decoding and stuff
Free the page
goto repeat
And I want it to go faster:
kmalloc a buffer
DMA-map the buffer
repeat:
Post a Recv for that buffer
Recv WR completes
DMA-sync the buffer
XDR decoding and stuff
goto repeat
On disconnect, the Recv flushes. The transport tear-down logic
takes care of DMA-unmapping and freeing the buffer.
> --b.
>
>>
>> * svc_rdma_wc_receive no longer has to DMA unmap the Receive buffer.
>> It has to DMA sync only the number of bytes that were received.
>>
>> * svc_rdma_build_arg_xdr no longer has to free a page in rq_pages
>> for each page in the Receive buffer, making it a constant-time
>> function.
>>
>> * The Receive buffer is now plugged directly into the rq_arg's
>> head[0].iov_vec, and can be larger than a page without spilling
>> over into rq_arg's page list. This enables simplification of
>> the RDMA Read path in subsequent patches.
>>
>> Signed-off-by: Chuck Lever <chuck.lever@xxxxxxxxxx>
>> ---
>> include/linux/sunrpc/svc_rdma.h | 4 -
>> net/sunrpc/xprtrdma/svc_rdma_recvfrom.c | 168 +++++++++++-------------------
>> net/sunrpc/xprtrdma/svc_rdma_rw.c | 32 ++----
>> net/sunrpc/xprtrdma/svc_rdma_sendto.c | 5 -
>> net/sunrpc/xprtrdma/svc_rdma_transport.c | 2
>> 5 files changed, 75 insertions(+), 136 deletions(-)
>>
>> diff --git a/include/linux/sunrpc/svc_rdma.h b/include/linux/sunrpc/svc_rdma.h
>> index f0bd0b6d..01baabf 100644
>> --- a/include/linux/sunrpc/svc_rdma.h
>> +++ b/include/linux/sunrpc/svc_rdma.h
>> @@ -148,12 +148,12 @@ struct svc_rdma_recv_ctxt {
>> struct list_head rc_list;
>> struct ib_recv_wr rc_recv_wr;
>> struct ib_cqe rc_cqe;
>> + struct ib_sge rc_recv_sge;
>> + void *rc_recv_buf;
>> struct xdr_buf rc_arg;
>> u32 rc_byte_len;
>> unsigned int rc_page_count;
>> unsigned int rc_hdr_count;
>> - struct ib_sge rc_sges[1 +
>> - RPCRDMA_MAX_INLINE_THRESH / PAGE_SIZE];
>> struct page *rc_pages[RPCSVC_MAXPAGES];
>> };
>>
>> diff --git a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
>> index d9fef52..d4ccd1c 100644
>> --- a/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
>> +++ b/net/sunrpc/xprtrdma/svc_rdma_recvfrom.c
>> @@ -117,6 +117,43 @@
>> rc_list);
>> }
>>
>> +static struct svc_rdma_recv_ctxt *
>> +svc_rdma_recv_ctxt_alloc(struct svcxprt_rdma *rdma)
>> +{
>> + struct svc_rdma_recv_ctxt *ctxt;
>> + dma_addr_t addr;
>> + void *buffer;
>> +
>> + ctxt = kmalloc(sizeof(*ctxt), GFP_KERNEL);
>> + if (!ctxt)
>> + goto fail0;
>> + buffer = kmalloc(rdma->sc_max_req_size, GFP_KERNEL);
>> + if (!buffer)
>> + goto fail1;
>> + addr = ib_dma_map_single(rdma->sc_pd->device, buffer,
>> + rdma->sc_max_req_size, DMA_FROM_DEVICE);
>> + if (ib_dma_mapping_error(rdma->sc_pd->device, addr))
>> + goto fail2;
>> +
>> + ctxt->rc_recv_wr.next = NULL;
>> + ctxt->rc_recv_wr.wr_cqe = &ctxt->rc_cqe;
>> + ctxt->rc_recv_wr.sg_list = &ctxt->rc_recv_sge;
>> + ctxt->rc_recv_wr.num_sge = 1;
>> + ctxt->rc_cqe.done = svc_rdma_wc_receive;
>> + ctxt->rc_recv_sge.addr = addr;
>> + ctxt->rc_recv_sge.length = rdma->sc_max_req_size;
>> + ctxt->rc_recv_sge.lkey = rdma->sc_pd->local_dma_lkey;
>> + ctxt->rc_recv_buf = buffer;
>> + return ctxt;
>> +
>> +fail2:
>> + kfree(buffer);
>> +fail1:
>> + kfree(ctxt);
>> +fail0:
>> + return NULL;
>> +}
>> +
>> /**
>> * svc_rdma_recv_ctxts_destroy - Release all recv_ctxt's for an xprt
>> * @rdma: svcxprt_rdma being torn down
>> @@ -128,6 +165,11 @@ void svc_rdma_recv_ctxts_destroy(struct svcxprt_rdma *rdma)
>>
>> while ((ctxt = svc_rdma_next_recv_ctxt(&rdma->sc_recv_ctxts))) {
>> list_del(&ctxt->rc_list);
>> + ib_dma_unmap_single(rdma->sc_pd->device,
>> + ctxt->rc_recv_sge.addr,
>> + ctxt->rc_recv_sge.length,
>> + DMA_FROM_DEVICE);
>> + kfree(ctxt->rc_recv_buf);
>> kfree(ctxt);
>> }
>> }
>> @@ -145,32 +187,18 @@ void svc_rdma_recv_ctxts_destroy(struct svcxprt_rdma *rdma)
>> spin_unlock(&rdma->sc_recv_lock);
>>
>> out:
>> - ctxt->rc_recv_wr.num_sge = 0;
>> ctxt->rc_page_count = 0;
>> return ctxt;
>>
>> out_empty:
>> spin_unlock(&rdma->sc_recv_lock);
>>
>> - ctxt = kmalloc(sizeof(*ctxt), GFP_KERNEL);
>> + ctxt = svc_rdma_recv_ctxt_alloc(rdma);
>> if (!ctxt)
>> return NULL;
>> goto out;
>> }
>>
>> -static void svc_rdma_recv_ctxt_unmap(struct svcxprt_rdma *rdma,
>> - struct svc_rdma_recv_ctxt *ctxt)
>> -{
>> - struct ib_device *device = rdma->sc_cm_id->device;
>> - int i;
>> -
>> - for (i = 0; i < ctxt->rc_recv_wr.num_sge; i++)
>> - ib_dma_unmap_page(device,
>> - ctxt->rc_sges[i].addr,
>> - ctxt->rc_sges[i].length,
>> - DMA_FROM_DEVICE);
>> -}
>> -
>> /**
>> * svc_rdma_recv_ctxt_put - Return recv_ctxt to free list
>> * @rdma: controlling svcxprt_rdma
>> @@ -191,46 +219,14 @@ void svc_rdma_recv_ctxt_put(struct svcxprt_rdma *rdma,
>>
>> static int svc_rdma_post_recv(struct svcxprt_rdma *rdma)
>> {
>> - struct ib_device *device = rdma->sc_cm_id->device;
>> struct svc_rdma_recv_ctxt *ctxt;
>> struct ib_recv_wr *bad_recv_wr;
>> - int sge_no, buflen, ret;
>> - struct page *page;
>> - dma_addr_t pa;
>> + int ret;
>>
>> ctxt = svc_rdma_recv_ctxt_get(rdma);
>> if (!ctxt)
>> return -ENOMEM;
>>
>> - buflen = 0;
>> - ctxt->rc_cqe.done = svc_rdma_wc_receive;
>> - for (sge_no = 0; buflen < rdma->sc_max_req_size; sge_no++) {
>> - if (sge_no >= rdma->sc_max_sge) {
>> - pr_err("svcrdma: Too many sges (%d)\n", sge_no);
>> - goto err_put_ctxt;
>> - }
>> -
>> - page = alloc_page(GFP_KERNEL);
>> - if (!page)
>> - goto err_put_ctxt;
>> - ctxt->rc_pages[sge_no] = page;
>> - ctxt->rc_page_count++;
>> -
>> - pa = ib_dma_map_page(device, ctxt->rc_pages[sge_no],
>> - 0, PAGE_SIZE, DMA_FROM_DEVICE);
>> - if (ib_dma_mapping_error(device, pa))
>> - goto err_put_ctxt;
>> - ctxt->rc_sges[sge_no].addr = pa;
>> - ctxt->rc_sges[sge_no].length = PAGE_SIZE;
>> - ctxt->rc_sges[sge_no].lkey = rdma->sc_pd->local_dma_lkey;
>> - ctxt->rc_recv_wr.num_sge++;
>> -
>> - buflen += PAGE_SIZE;
>> - }
>> - ctxt->rc_recv_wr.next = NULL;
>> - ctxt->rc_recv_wr.sg_list = &ctxt->rc_sges[0];
>> - ctxt->rc_recv_wr.wr_cqe = &ctxt->rc_cqe;
>> -
>> svc_xprt_get(&rdma->sc_xprt);
>> ret = ib_post_recv(rdma->sc_qp, &ctxt->rc_recv_wr, &bad_recv_wr);
>> trace_svcrdma_post_recv(&ctxt->rc_recv_wr, ret);
>> @@ -238,12 +234,7 @@ static int svc_rdma_post_recv(struct svcxprt_rdma *rdma)
>> goto err_post;
>> return 0;
>>
>> -err_put_ctxt:
>> - svc_rdma_recv_ctxt_unmap(rdma, ctxt);
>> - svc_rdma_recv_ctxt_put(rdma, ctxt);
>> - return -ENOMEM;
>> err_post:
>> - svc_rdma_recv_ctxt_unmap(rdma, ctxt);
>> svc_rdma_recv_ctxt_put(rdma, ctxt);
>> svc_xprt_put(&rdma->sc_xprt);
>> return ret;
>> @@ -289,7 +280,6 @@ static void svc_rdma_wc_receive(struct ib_cq *cq, struct ib_wc *wc)
>>
>> /* WARNING: Only wc->wr_cqe and wc->status are reliable */
>> ctxt = container_of(cqe, struct svc_rdma_recv_ctxt, rc_cqe);
>> - svc_rdma_recv_ctxt_unmap(rdma, ctxt);
>>
>> if (wc->status != IB_WC_SUCCESS)
>> goto flushed;
>> @@ -299,6 +289,10 @@ static void svc_rdma_wc_receive(struct ib_cq *cq, struct ib_wc *wc)
>>
>> /* All wc fields are now known to be valid */
>> ctxt->rc_byte_len = wc->byte_len;
>> + ib_dma_sync_single_for_cpu(rdma->sc_pd->device,
>> + ctxt->rc_recv_sge.addr,
>> + wc->byte_len, DMA_FROM_DEVICE);
>> +
>> spin_lock(&rdma->sc_rq_dto_lock);
>> list_add_tail(&ctxt->rc_list, &rdma->sc_rq_dto_q);
>> spin_unlock(&rdma->sc_rq_dto_lock);
>> @@ -339,64 +333,22 @@ void svc_rdma_flush_recv_queues(struct svcxprt_rdma *rdma)
>> }
>> }
>>
>> -/*
>> - * Replace the pages in the rq_argpages array with the pages from the SGE in
>> - * the RDMA_RECV completion. The SGL should contain full pages up until the
>> - * last one.
>> - */
>> static void svc_rdma_build_arg_xdr(struct svc_rqst *rqstp,
>> struct svc_rdma_recv_ctxt *ctxt)
>> {
>> - struct page *page;
>> - int sge_no;
>> - u32 len;
>> -
>> - /* The reply path assumes the Call's transport header resides
>> - * in rqstp->rq_pages[0].
>> - */
>> - page = ctxt->rc_pages[0];
>> - put_page(rqstp->rq_pages[0]);
>> - rqstp->rq_pages[0] = page;
>> -
>> - /* Set up the XDR head */
>> - rqstp->rq_arg.head[0].iov_base = page_address(page);
>> - rqstp->rq_arg.head[0].iov_len =
>> - min_t(size_t, ctxt->rc_byte_len, ctxt->rc_sges[0].length);
>> - rqstp->rq_arg.len = ctxt->rc_byte_len;
>> - rqstp->rq_arg.buflen = ctxt->rc_byte_len;
>> -
>> - /* Compute bytes past head in the SGL */
>> - len = ctxt->rc_byte_len - rqstp->rq_arg.head[0].iov_len;
>> -
>> - /* If data remains, store it in the pagelist */
>> - rqstp->rq_arg.page_len = len;
>> - rqstp->rq_arg.page_base = 0;
>> -
>> - sge_no = 1;
>> - while (len && sge_no < ctxt->rc_recv_wr.num_sge) {
>> - page = ctxt->rc_pages[sge_no];
>> - put_page(rqstp->rq_pages[sge_no]);
>> - rqstp->rq_pages[sge_no] = page;
>> - len -= min_t(u32, len, ctxt->rc_sges[sge_no].length);
>> - sge_no++;
>> - }
>> - ctxt->rc_hdr_count = sge_no;
>> - rqstp->rq_respages = &rqstp->rq_pages[sge_no];
>> + struct xdr_buf *arg = &rqstp->rq_arg;
>> +
>> + arg->head[0].iov_base = ctxt->rc_recv_buf;
>> + arg->head[0].iov_len = ctxt->rc_byte_len;
>> + arg->tail[0].iov_base = NULL;
>> + arg->tail[0].iov_len = 0;
>> + arg->page_len = 0;
>> + arg->page_base = 0;
>> + arg->buflen = ctxt->rc_byte_len;
>> + arg->len = ctxt->rc_byte_len;
>> +
>> + rqstp->rq_respages = &rqstp->rq_pages[0];
>> rqstp->rq_next_page = rqstp->rq_respages + 1;
>> -
>> - /* If not all pages were used from the SGL, free the remaining ones */
>> - while (sge_no < ctxt->rc_recv_wr.num_sge) {
>> - page = ctxt->rc_pages[sge_no++];
>> - put_page(page);
>> - }
>> -
>> - /* @ctxt's pages have all been released or moved to @rqstp->rq_pages.
>> - */
>> - ctxt->rc_page_count = 0;
>> -
>> - /* Set up tail */
>> - rqstp->rq_arg.tail[0].iov_base = NULL;
>> - rqstp->rq_arg.tail[0].iov_len = 0;
>> }
>>
>> /* This accommodates the largest possible Write chunk,
>> diff --git a/net/sunrpc/xprtrdma/svc_rdma_rw.c b/net/sunrpc/xprtrdma/svc_rdma_rw.c
>> index 8242aa3..ce3ea84 100644
>> --- a/net/sunrpc/xprtrdma/svc_rdma_rw.c
>> +++ b/net/sunrpc/xprtrdma/svc_rdma_rw.c
>> @@ -718,15 +718,14 @@ static int svc_rdma_build_normal_read_chunk(struct svc_rqst *rqstp,
>> struct svc_rdma_recv_ctxt *head = info->ri_readctxt;
>> int ret;
>>
>> - info->ri_pageno = head->rc_hdr_count;
>> - info->ri_pageoff = 0;
>> -
>> ret = svc_rdma_build_read_chunk(rqstp, info, p);
>> if (ret < 0)
>> goto out;
>>
>> trace_svcrdma_encode_read(info->ri_chunklen, info->ri_position);
>>
>> + head->rc_hdr_count = 0;
>> +
>> /* Split the Receive buffer between the head and tail
>> * buffers at Read chunk's position. XDR roundup of the
>> * chunk is not included in either the pagelist or in
>> @@ -775,9 +774,6 @@ static int svc_rdma_build_pz_read_chunk(struct svc_rqst *rqstp,
>> struct svc_rdma_recv_ctxt *head = info->ri_readctxt;
>> int ret;
>>
>> - info->ri_pageno = head->rc_hdr_count - 1;
>> - info->ri_pageoff = offset_in_page(head->rc_byte_len);
>> -
>> ret = svc_rdma_build_read_chunk(rqstp, info, p);
>> if (ret < 0)
>> goto out;
>> @@ -787,20 +783,13 @@ static int svc_rdma_build_pz_read_chunk(struct svc_rqst *rqstp,
>> head->rc_arg.len += info->ri_chunklen;
>> head->rc_arg.buflen += info->ri_chunklen;
>>
>> - if (head->rc_arg.buflen <= head->rc_sges[0].length) {
>> - /* Transport header and RPC message fit entirely
>> - * in page where head iovec resides.
>> - */
>> - head->rc_arg.head[0].iov_len = info->ri_chunklen;
>> - } else {
>> - /* Transport header and part of RPC message reside
>> - * in the head iovec's page.
>> - */
>> - head->rc_arg.head[0].iov_len =
>> - head->rc_sges[0].length - head->rc_byte_len;
>> - head->rc_arg.page_len =
>> - info->ri_chunklen - head->rc_arg.head[0].iov_len;
>> - }
>> + head->rc_hdr_count = 1;
>> + head->rc_arg.head[0].iov_base = page_address(head->rc_pages[0]);
>> + head->rc_arg.head[0].iov_len = min_t(size_t, PAGE_SIZE,
>> + info->ri_chunklen);
>> +
>> + head->rc_arg.page_len = info->ri_chunklen -
>> + head->rc_arg.head[0].iov_len;
>>
>> out:
>> return ret;
>> @@ -834,7 +823,6 @@ int svc_rdma_recv_read_chunk(struct svcxprt_rdma *rdma, struct svc_rqst *rqstp,
>> * head->rc_arg. Pages involved with RDMA Read I/O are
>> * transferred there.
>> */
>> - head->rc_page_count = head->rc_hdr_count;
>> head->rc_arg.head[0] = rqstp->rq_arg.head[0];
>> head->rc_arg.tail[0] = rqstp->rq_arg.tail[0];
>> head->rc_arg.pages = head->rc_pages;
>> @@ -847,6 +835,8 @@ int svc_rdma_recv_read_chunk(struct svcxprt_rdma *rdma, struct svc_rqst *rqstp,
>> if (!info)
>> return -ENOMEM;
>> info->ri_readctxt = head;
>> + info->ri_pageno = 0;
>> + info->ri_pageoff = 0;
>>
>> info->ri_position = be32_to_cpup(p + 1);
>> if (info->ri_position)
>> diff --git a/net/sunrpc/xprtrdma/svc_rdma_sendto.c b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
>> index cbbde70..b27b597 100644
>> --- a/net/sunrpc/xprtrdma/svc_rdma_sendto.c
>> +++ b/net/sunrpc/xprtrdma/svc_rdma_sendto.c
>> @@ -629,10 +629,7 @@ int svc_rdma_sendto(struct svc_rqst *rqstp)
>> struct page *res_page;
>> int ret;
>>
>> - /* Find the call's chunk lists to decide how to send the reply.
>> - * Receive places the Call's xprt header at the start of page 0.
>> - */
>> - rdma_argp = page_address(rqstp->rq_pages[0]);
>> + rdma_argp = rctxt->rc_recv_buf;
>> svc_rdma_get_write_arrays(rdma_argp, &wr_lst, &rp_ch);
>>
>> /* Create the RDMA response header. xprt->xpt_mutex,
>> diff --git a/net/sunrpc/xprtrdma/svc_rdma_transport.c b/net/sunrpc/xprtrdma/svc_rdma_transport.c
>> index 20abd3a..333c432 100644
>> --- a/net/sunrpc/xprtrdma/svc_rdma_transport.c
>> +++ b/net/sunrpc/xprtrdma/svc_rdma_transport.c
>> @@ -670,7 +670,7 @@ static struct svc_xprt *svc_rdma_accept(struct svc_xprt *xprt)
>> qp_attr.cap.max_send_wr = newxprt->sc_sq_depth - ctxts;
>> qp_attr.cap.max_recv_wr = rq_depth;
>> qp_attr.cap.max_send_sge = newxprt->sc_max_sge;
>> - qp_attr.cap.max_recv_sge = newxprt->sc_max_sge;
>> + qp_attr.cap.max_recv_sge = 1;
>> qp_attr.sq_sig_type = IB_SIGNAL_REQ_WR;
>> qp_attr.qp_type = IB_QPT_RC;
>> qp_attr.send_cq = newxprt->sc_sq_cq;
> --
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