From patchwork Mon Jan 14 13:51:52 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Anthony PERARD X-Patchwork-Id: 1024587 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Authentication-Results: ozlabs.org; spf=pass (mailfrom) smtp.mailfrom=nongnu.org (client-ip=209.51.188.17; helo=lists.gnu.org; envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org; receiver=) Authentication-Results: ozlabs.org; dmarc=none (p=none dis=none) header.from=citrix.com Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by ozlabs.org (Postfix) with ESMTPS id 43dbM94Kzpz9s2P for ; Tue, 15 Jan 2019 01:24:21 +1100 (AEDT) Received: from localhost ([127.0.0.1]:38204 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gj3A3-0000EM-E7 for incoming@patchwork.ozlabs.org; Mon, 14 Jan 2019 09:24:19 -0500 Received: from eggs.gnu.org ([209.51.188.92]:47401) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1gj2lp-0007Em-Gk for qemu-devel@nongnu.org; Mon, 14 Jan 2019 08:59:19 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gj2lo-0004vg-JK for qemu-devel@nongnu.org; Mon, 14 Jan 2019 08:59:17 -0500 Received: from smtp03.citrix.com ([162.221.156.55]:1402) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gj2lo-0004v3-BU for qemu-devel@nongnu.org; Mon, 14 Jan 2019 08:59:16 -0500 X-IronPort-AV: E=Sophos;i="5.56,477,1539648000"; d="scan'208";a="75507045" From: Anthony PERARD To: Date: Mon, 14 Jan 2019 13:51:52 +0000 Message-ID: <20190114135154.16826-24-anthony.perard@citrix.com> X-Mailer: git-send-email 2.20.1 In-Reply-To: <20190114135154.16826-1-anthony.perard@citrix.com> References: <20190114135154.16826-1-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, Peter Maydell Errors-To: qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org Sender: "Qemu-devel" 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 &&