From patchwork Thu Jan 10 13:49:16 2019 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Anthony PERARD X-Patchwork-Id: 10755927 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 DDAA76C2 for ; Thu, 10 Jan 2019 14:23:41 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id C8540299A7 for ; Thu, 10 Jan 2019 14:23:41 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id C6865299AA; Thu, 10 Jan 2019 14:23:41 +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 2E645299CD for ; Thu, 10 Jan 2019 14:23:41 +0000 (UTC) Received: from localhost ([127.0.0.1]:33949 helo=lists.gnu.org) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ghbFE-0006qG-Av for patchwork-qemu-devel@patchwork.kernel.org; Thu, 10 Jan 2019 09:23:40 -0500 Received: from eggs.gnu.org ([209.51.188.92]:57997) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ghb5B-0005zL-T4 for qemu-devel@nongnu.org; Thu, 10 Jan 2019 09:13:19 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1gharN-0002Ly-Ky for qemu-devel@nongnu.org; Thu, 10 Jan 2019 08:59:03 -0500 Received: from smtp03.citrix.com ([162.221.156.55]:12008) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1gharN-0001xV-9N for qemu-devel@nongnu.org; Thu, 10 Jan 2019 08:59:01 -0500 X-IronPort-AV: E=Sophos;i="5.56,461,1539648000"; d="scan'208";a="75263668" From: Anthony PERARD To: Date: Thu, 10 Jan 2019 13:49:16 +0000 Message-ID: <20190110134917.16425-25-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 24/25] xen-block: improve response latency 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 If the I/O ring is full, the guest cannot send any more requests until some responses are sent. Only sending all available responses just before checking for new work does not leave much time for the guest to supply new work, so this will cause stalls if the ring gets full. Also, not completing reads as soon as possible adds latency to the guest. To alleviate that, complete IO requests as soon as they come back. xen_block_send_response() already returns a value indicating whether a notify should be sent, which is all the batching we need. 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 | 56 +++++++++++----------------------- 1 file changed, 18 insertions(+), 38 deletions(-) diff --git a/hw/block/dataplane/xen-block.c b/hw/block/dataplane/xen-block.c index acd23a74a8..35bfccfba7 100644 --- a/hw/block/dataplane/xen-block.c +++ b/hw/block/dataplane/xen-block.c @@ -55,11 +55,9 @@ struct XenBlockDataPlane { blkif_back_rings_t rings; int more_work; QLIST_HEAD(inflight_head, XenBlockRequest) inflight; - QLIST_HEAD(finished_head, XenBlockRequest) finished; QLIST_HEAD(freelist_head, XenBlockRequest) freelist; int requests_total; int requests_inflight; - int requests_finished; unsigned int max_requests; BlockBackend *blk; QEMUBH *bh; @@ -116,12 +114,10 @@ static void xen_block_finish_request(XenBlockRequest *request) XenBlockDataPlane *dataplane = request->dataplane; QLIST_REMOVE(request, list); - QLIST_INSERT_HEAD(&dataplane->finished, request, list); dataplane->requests_inflight--; - dataplane->requests_finished++; } -static void xen_block_release_request(XenBlockRequest *request, bool finish) +static void xen_block_release_request(XenBlockRequest *request) { XenBlockDataPlane *dataplane = request->dataplane; @@ -129,11 +125,7 @@ static void xen_block_release_request(XenBlockRequest *request, bool finish) reset_request(request); request->dataplane = dataplane; QLIST_INSERT_HEAD(&dataplane->freelist, request, list); - if (finish) { - dataplane->requests_finished--; - } else { - dataplane->requests_inflight--; - } + dataplane->requests_inflight--; } /* @@ -248,6 +240,7 @@ static int xen_block_copy_request(XenBlockRequest *request) } static int xen_block_do_aio(XenBlockRequest *request); +static int xen_block_send_response(XenBlockRequest *request); static void xen_block_complete_aio(void *opaque, int ret) { @@ -312,6 +305,18 @@ static void xen_block_complete_aio(void *opaque, int ret) default: break; } + if (xen_block_send_response(request)) { + Error *local_err = NULL; + + xen_device_notify_event_channel(dataplane->xendev, + dataplane->event_channel, + &local_err); + if (local_err) { + error_report_err(local_err); + } + } + xen_block_release_request(request); + qemu_bh_schedule(dataplane->bh); done: @@ -419,7 +424,7 @@ static int xen_block_do_aio(XenBlockRequest *request) return -1; } -static int xen_block_send_response_one(XenBlockRequest *request) +static int xen_block_send_response(XenBlockRequest *request) { XenBlockDataPlane *dataplane = request->dataplane; int send_notify = 0; @@ -474,29 +479,6 @@ static int xen_block_send_response_one(XenBlockRequest *request) return send_notify; } -/* walk finished list, send outstanding responses, free requests */ -static void xen_block_send_response_all(XenBlockDataPlane *dataplane) -{ - XenBlockRequest *request; - int send_notify = 0; - - while (!QLIST_EMPTY(&dataplane->finished)) { - request = QLIST_FIRST(&dataplane->finished); - send_notify += xen_block_send_response_one(request); - xen_block_release_request(request, true); - } - if (send_notify) { - Error *local_err = NULL; - - xen_device_notify_event_channel(dataplane->xendev, - dataplane->event_channel, - &local_err); - if (local_err) { - error_report_err(local_err); - } - } -} - static int xen_block_get_request(XenBlockDataPlane *dataplane, XenBlockRequest *request, RING_IDX rc) { @@ -547,7 +529,6 @@ static void xen_block_handle_requests(XenBlockDataPlane *dataplane) rp = dataplane->rings.common.sring->req_prod; 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 @@ -591,7 +572,7 @@ static void xen_block_handle_requests(XenBlockDataPlane *dataplane) break; }; - if (xen_block_send_response_one(request)) { + if (xen_block_send_response(request)) { Error *local_err = NULL; xen_device_notify_event_channel(dataplane->xendev, @@ -601,7 +582,7 @@ static void xen_block_handle_requests(XenBlockDataPlane *dataplane) error_report_err(local_err); } } - xen_block_release_request(request, false); + xen_block_release_request(request); continue; } @@ -657,7 +638,6 @@ XenBlockDataPlane *xen_block_dataplane_create(XenDevice *xendev, dataplane->file_size = blk_getlength(dataplane->blk); QLIST_INIT(&dataplane->inflight); - QLIST_INIT(&dataplane->finished); QLIST_INIT(&dataplane->freelist); if (iothread) {