From patchwork Thu Jan 10 13:49:15 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Anthony PERARD X-Patchwork-Id: 10755907 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 9A63917E1 for ; Thu, 10 Jan 2019 14:20:36 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 8365A29960 for ; Thu, 10 Jan 2019 14:20:36 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 4CB4C2997F; Thu, 10 Jan 2019 14:20:36 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI autolearn=ham version=3.3.1 Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1 with cipher AES256-SHA (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 77BD0298CF for ; Thu, 10 Jan 2019 14:20:26 +0000 (UTC) Received: from localhost ([127.0.0.1]:33179 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ghbC4-00047k-84 for patchwork-qemu-devel@patchwork.kernel.org; Thu, 10 Jan 2019 09:20:24 -0500 Received: from eggs.gnu.org ([209.51.188.92]:57997) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ghb5A-0005zL-Hy for qemu-devel@nongnu.org; Thu, 10 Jan 2019 09:13:17 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gharW-0002Rf-Q3 for qemu-devel@nongnu.org; Thu, 10 Jan 2019 08:59:11 -0500 Received: from smtp03.citrix.com ([162.221.156.55]:12049) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gharW-0002QK-Fn for qemu-devel@nongnu.org; Thu, 10 Jan 2019 08:59:10 -0500 X-IronPort-AV: E=Sophos;i="5.56,461,1539648000"; d="scan'208";a="75263686" From: Anthony PERARD To: Date: Thu, 10 Jan 2019 13:49:15 +0000 Message-ID: <20190110134917.16425-24-anthony.perard@citrix.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190110134917.16425-1-anthony.perard@citrix.com> References: <20190110134917.16425-1-anthony.perard@citrix.com> MIME-Version: 1.0 X-detected-operating-system: by eggs.gnu.org: Genre and OS details not recognized. X-Received-From: 162.221.156.55 Subject: [Qemu-devel] [PULL 23/25] xen-block: improve batching behaviour X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Anthony PERARD , xen-devel@lists.xenproject.org, Paul Durrant , Tim Smith Errors-To: qemu-devel-bounces+patchwork-qemu-devel=patchwork.kernel.org@nongnu.org Sender: "Qemu-devel" X-Virus-Scanned: ClamAV using ClamSMTP From: Tim Smith When I/O consists of many small requests, performance is improved by batching them together in a single io_submit() call. When there are relatively few requests, the extra overhead is not worth it. This introduces a check to start batching I/O requests via blk_io_plug()/ blk_io_unplug() in an amount proportional to the number which were already in flight at the time we started reading the ring. Signed-off-by: Tim Smith Re-based and commit comment adjusted. Signed-off-by: Paul Durrant Acked-by: Anthony PERARD Signed-off-by: Anthony PERARD --- hw/block/dataplane/xen-block.c | 35 ++++++++++++++++++++++++++++++++++ 1 file changed, 35 insertions(+) diff --git a/hw/block/dataplane/xen-block.c b/hw/block/dataplane/xen-block.c index 8e3965e171..acd23a74a8 100644 --- a/hw/block/dataplane/xen-block.c +++ b/hw/block/dataplane/xen-block.c @@ -528,10 +528,18 @@ static int xen_block_get_request(XenBlockDataPlane *dataplane, return 0; } +/* + * Threshold of in-flight requests above which we will start using + * blk_io_plug()/blk_io_unplug() to batch requests. + */ +#define IO_PLUG_THRESHOLD 1 + static void xen_block_handle_requests(XenBlockDataPlane *dataplane) { RING_IDX rc, rp; XenBlockRequest *request; + int inflight_atstart = dataplane->requests_inflight; + int batched = 0; dataplane->more_work = 0; @@ -540,6 +548,18 @@ static void xen_block_handle_requests(XenBlockDataPlane *dataplane) xen_rmb(); /* Ensure we see queued requests up to 'rp'. */ xen_block_send_response_all(dataplane); + /* + * If there was more than IO_PLUG_THRESHOLD requests in flight + * when we got here, this is an indication that there the bottleneck + * is below us, so it's worth beginning to batch up I/O requests + * rather than submitting them immediately. The maximum number + * of requests we're willing to batch is the number already in + * flight, so it can grow up to max_requests when the bottleneck + * is below us. + */ + if (inflight_atstart > IO_PLUG_THRESHOLD) { + blk_io_plug(dataplane->blk); + } while (rc != rp) { /* pull request from ring */ if (RING_REQUEST_CONS_OVERFLOW(&dataplane->rings.common, rc)) { @@ -585,7 +605,22 @@ static void xen_block_handle_requests(XenBlockDataPlane *dataplane) continue; } + if (inflight_atstart > IO_PLUG_THRESHOLD && + batched >= inflight_atstart) { + blk_io_unplug(dataplane->blk); + } xen_block_do_aio(request); + if (inflight_atstart > IO_PLUG_THRESHOLD) { + if (batched >= inflight_atstart) { + blk_io_plug(dataplane->blk); + batched = 0; + } else { + batched++; + } + } + } + if (inflight_atstart > IO_PLUG_THRESHOLD) { + blk_io_unplug(dataplane->blk); } if (dataplane->more_work &&