From patchwork Fri Feb 28 00:32:16 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Chuck Lever X-Patchwork-Id: 11411295 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id E939C924 for ; Fri, 28 Feb 2020 00:32:19 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id C8DEA246A0 for ; Fri, 28 Feb 2020 00:32:19 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=fail reason="signature verification failed" (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="JgGJRtpm" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730375AbgB1AcT (ORCPT ); Thu, 27 Feb 2020 19:32:19 -0500 Received: from mail-pl1-f194.google.com ([209.85.214.194]:43502 "EHLO mail-pl1-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730253AbgB1AcT (ORCPT ); Thu, 27 Feb 2020 19:32:19 -0500 Received: by mail-pl1-f194.google.com with SMTP id p11so490220plq.10; Thu, 27 Feb 2020 16:32:18 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=sender:subject:from:to:cc:date:message-id:in-reply-to:references :user-agent:mime-version:content-transfer-encoding; bh=Rh0J7J+tmI9ibvdcsm+0y9mwMYxxyAhrYZdwv/dpsVs=; b=JgGJRtpmRQYq4WDLgxCITaAj2ShvrCED1EkjwcpTiEr/6r5/0OPWOZ9k9lc31K0sBN d96QEG2Ed9x3bLuz7YP6t0ZYhWj7PPdGOL6ZU/4BWgsxTjYymn5NmXbt5eH600h0xcvo ekN8P90C7/XW//n2WG7eyjacCSCF7OIB/y9/KF4wR29ebax1TIOL7ptTFx4q51Qgk+xp TSsHPFxzBFt6mqq8b0uc11Fpy2wJq46WKBcDw5Nw16PYSlyCty+6s55vjNWDaXMnpMP0 ICCUcbKGsHWgvh1lWFxCXVtDOCR3UsFGG6FELqphsWVZ2eJUpJjFTsDIFCbci+R8wqHq o10A== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:sender:subject:from:to:cc:date:message-id :in-reply-to:references:user-agent:mime-version :content-transfer-encoding; bh=Rh0J7J+tmI9ibvdcsm+0y9mwMYxxyAhrYZdwv/dpsVs=; b=IxaLRZHifIxwHjgx3PFZxmfLfWy/3JYcXErt1HpIpkCK9Vcsqdevb97yV28yqJsxKc pS6IqnMnF9y1rfKdeJR/dEv2FODCmlANfJzwhL6AlVhgV8xTOXYuux1rq+husbb8mlwB /JqxUYEuV1uVN4OropNVrqykHEAn3op586PlyeIQLSrGyRRmHzQeHKhuTasL3bdjjUaH G/c+kmWqdr+PCADb6YDE85rMuJSyj6H1lfmhoVsUQ+VWGMRUXkzURY2UL3pKrjfWr7Br NLDxx4NCgsFdF+4R+oCcyzrwrd0hVJAdlwulZs4FFmZeSxYzf943AMz/yKQDXO73pxLx niSQ== X-Gm-Message-State: APjAAAVSyVJSCqFDmmqVIF17pMj8yI3cB+2QIhS0jI7w1nJyYQ2q7Cu5 V2cqRd89HCv2tDmBwW/w7gLx2FqW7hA= X-Google-Smtp-Source: APXvYqzEK+YIRCXyESRiVTv9OYqSRB+MClMUSy6tM2tGMvj6K/bEJMqF8h7CEJ/2t785gOnMdIQ42w== X-Received: by 2002:a17:90a:da04:: with SMTP id e4mr1631372pjv.26.1582849937969; Thu, 27 Feb 2020 16:32:17 -0800 (PST) Received: from seurat29.1015granger.net (ip-184-250-247-225.sanjca.spcsdns.net. [184.250.247.225]) by smtp.gmail.com with ESMTPSA id z13sm7995590pge.29.2020.02.27.16.32.16 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 27 Feb 2020 16:32:17 -0800 (PST) Subject: [PATCH v1 16/16] svcrdma: Avoid DMA mapping small RPC Replies From: Chuck Lever To: bfields@fieldses.org Cc: linux-nfs@vger.kernel.org, linux-rdma@vger.kernel.org Date: Thu, 27 Feb 2020 19:32:16 -0500 Message-ID: <158284993622.38468.2163113637049774961.stgit@seurat29.1015granger.net> In-Reply-To: <158284930886.38468.17045380766660946827.stgit@seurat29.1015granger.net> References: <158284930886.38468.17045380766660946827.stgit@seurat29.1015granger.net> User-Agent: StGit/unknown-version MIME-Version: 1.0 Sender: linux-nfs-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-nfs@vger.kernel.org On some platforms, DMA mapping part of a page is more costly than copying bytes. Indeed, not involving the I/O MMU can help the RPC/RDMA transport scale better for tiny I/Os across more RDMA devices. This is because interaction with the I/O MMU is eliminated for each of these small I/Os. Without the explicit unmapping, the NIC no longer needs to do a costly internal TLB shoot down for buffers that are just a handful of bytes. Since pull-up is now a more a frequent operation, I've introduced a trace point in the pull-up path. It can be used for debugging or user-space tools that count pull-up frequency. Signed-off-by: Chuck Lever --- include/trace/events/rpcrdma.h | 18 ++++++++++++++++++ net/sunrpc/xprtrdma/svc_rdma_sendto.c | 15 ++++++++++++++- 2 files changed, 32 insertions(+), 1 deletion(-) diff --git a/include/trace/events/rpcrdma.h b/include/trace/events/rpcrdma.h index 74b68547eefb..9238d233f8cf 100644 --- a/include/trace/events/rpcrdma.h +++ b/include/trace/events/rpcrdma.h @@ -1639,6 +1639,24 @@ TRACE_EVENT(svcrdma_dma_map_rwctx, ) ); +TRACE_EVENT(svcrdma_send_pullup, + TP_PROTO( + unsigned int len + ), + + TP_ARGS(len), + + TP_STRUCT__entry( + __field(unsigned int, len) + ), + + TP_fast_assign( + __entry->len = len; + ), + + TP_printk("len=%u", __entry->len) +); + TRACE_EVENT(svcrdma_send_failed, TP_PROTO( const struct svc_rqst *rqst, diff --git a/net/sunrpc/xprtrdma/svc_rdma_sendto.c b/net/sunrpc/xprtrdma/svc_rdma_sendto.c index 9a7317bc54c9..3669a41bf8b6 100644 --- a/net/sunrpc/xprtrdma/svc_rdma_sendto.c +++ b/net/sunrpc/xprtrdma/svc_rdma_sendto.c @@ -539,6 +539,7 @@ static int svc_rdma_dma_map_buf(struct svcxprt_rdma *rdma, /** * svc_rdma_pull_up_needed - Determine whether to use pull-up * @rdma: controlling transport + * @sctxt: send_ctxt for the Send WR * @rctxt: Write and Reply chunks provided by client * @xdr: xdr_buf containing RPC message to transmit * @@ -547,11 +548,22 @@ static int svc_rdma_dma_map_buf(struct svcxprt_rdma *rdma, * %false otherwise */ static bool svc_rdma_pull_up_needed(struct svcxprt_rdma *rdma, + struct svc_rdma_send_ctxt *sctxt, const struct svc_rdma_recv_ctxt *rctxt, struct xdr_buf *xdr) { int elements; + /* For small messages, copying bytes is cheaper than DMA + * mapping. + */ + if (sctxt->sc_hdrbuf.len + xdr->len < + RPCRDMA_V1_DEF_INLINE_SIZE >> 1) + return true; + + /* Check whether the xdr_buf has more elements than can + * fit in a single RDMA Send. + */ /* xdr->head */ elements = 1; @@ -634,6 +646,7 @@ static int svc_rdma_pull_up_reply_msg(struct svcxprt_rdma *rdma, memcpy(dst, tailbase, taillen); sctxt->sc_sges[0].length += xdr->len; + trace_svcrdma_send_pullup(sctxt->sc_sges[0].length); return 0; } @@ -667,7 +680,7 @@ int svc_rdma_map_reply_msg(struct svcxprt_rdma *rdma, if (rctxt && rctxt->rc_reply_chunk) return 0; - if (svc_rdma_pull_up_needed(rdma, rctxt, xdr)) + if (svc_rdma_pull_up_needed(rdma, sctxt, rctxt, xdr)) return svc_rdma_pull_up_reply_msg(rdma, sctxt, rctxt, xdr); ++sctxt->sc_cur_sge_no;