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{ "id": 2227799, "url": "http://patchwork.ozlabs.org/api/1.1/covers/2227799/?format=api", "web_url": "http://patchwork.ozlabs.org/project/qemu-devel/cover/20260424-force_rcu-v4-0-feccfaca0568@rsg.ci.i.u-tokyo.ac.jp/", "project": { "id": 14, "url": "http://patchwork.ozlabs.org/api/1.1/projects/14/?format=api", "name": "QEMU Development", "link_name": "qemu-devel", "list_id": "qemu-devel.nongnu.org", "list_email": "qemu-devel@nongnu.org", "web_url": "", "scm_url": "", "webscm_url": "" }, "msgid": "<20260424-force_rcu-v4-0-feccfaca0568@rsg.ci.i.u-tokyo.ac.jp>", "date": "2026-04-24T09:27:05", "name": "[v4,0/6] virtio-gpu: Force RCU when unmapping blob", "submitter": { "id": 90980, "url": "http://patchwork.ozlabs.org/api/1.1/people/90980/?format=api", "name": "Akihiko Odaki", "email": "odaki@rsg.ci.i.u-tokyo.ac.jp" }, "mbox": "http://patchwork.ozlabs.org/project/qemu-devel/cover/20260424-force_rcu-v4-0-feccfaca0568@rsg.ci.i.u-tokyo.ac.jp/mbox/", "series": [ { "id": 501326, "url": "http://patchwork.ozlabs.org/api/1.1/series/501326/?format=api", "web_url": "http://patchwork.ozlabs.org/project/qemu-devel/list/?series=501326", "date": "2026-04-24T09:27:07", "name": "virtio-gpu: Force RCU when unmapping blob", "version": 4, "mbox": "http://patchwork.ozlabs.org/series/501326/mbox/" } ], "comments": "http://patchwork.ozlabs.org/api/covers/2227799/comments/", "headers": { "Return-Path": "<qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org>", "X-Original-To": "incoming@patchwork.ozlabs.org", "Delivered-To": "patchwork-incoming@legolas.ozlabs.org", "Authentication-Results": [ "legolas.ozlabs.org;\n\tdkim=fail reason=\"key not found in DNS\" header.d=rsg.ci.i.u-tokyo.ac.jp\n header.i=@rsg.ci.i.u-tokyo.ac.jp header.a=rsa-sha256 header.s=rs20250326\n header.b=pxhTFz/3;\n\tdkim-atps=neutral", "legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; helo=lists1p.gnu.org;\n envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org;\n receiver=patchwork.ozlabs.org)" ], "Received": [ "from lists1p.gnu.org (lists1p.gnu.org [209.51.188.17])\n\t(using TLSv1.2 with cipher ECDHE-ECDSA-AES256-GCM-SHA384 (256/256 bits))\n\t(No client certificate requested)\n\tby legolas.ozlabs.org (Postfix) with ESMTPS id 4g272t5ZCrz1xvV\n\tfor <incoming@patchwork.ozlabs.org>; Fri, 24 Apr 2026 19:29:42 +1000 (AEST)", "from localhost ([::1] helo=lists1p.gnu.org)\n\tby lists1p.gnu.org with esmtp (Exim 4.90_1)\n\t(envelope-from <qemu-devel-bounces@nongnu.org>)\n\tid 1wGCq1-0000L4-Kk; Fri, 24 Apr 2026 05:28:45 -0400", "from eggs.gnu.org ([2001:470:142:3::10])\n by lists1p.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256)\n (Exim 4.90_1) (envelope-from <odaki@rsg.ci.i.u-tokyo.ac.jp>)\n id 1wGCp5-0007Q7-02\n for qemu-devel@nongnu.org; Fri, 24 Apr 2026 05:27:43 -0400", "from www3579.sakura.ne.jp ([49.212.243.89])\n by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256)\n (Exim 4.90_1) (envelope-from <odaki@rsg.ci.i.u-tokyo.ac.jp>)\n id 1wGCoz-0007a9-Sl\n for qemu-devel@nongnu.org; Fri, 24 Apr 2026 05:27:42 -0400", "from h205.csg.ci.i.u-tokyo.ac.jp (h205.csg.ci.i.u-tokyo.ac.jp\n [133.11.54.205]) (authenticated bits=0)\n by www3579.sakura.ne.jp (8.16.1/8.16.1) with ESMTPSA id 63O9RHIc004358\n (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO);\n Fri, 24 Apr 2026 18:27:26 +0900 (JST)\n (envelope-from odaki@rsg.ci.i.u-tokyo.ac.jp)" ], "DKIM-Signature": "a=rsa-sha256; bh=lX2DrJ15GFa+OK9kpXU5Omtv6JD2l+5NZcELVoCPJXY=;\n c=relaxed/relaxed; d=rsg.ci.i.u-tokyo.ac.jp;\n h=From:Message-Id:To:Subject:Date;\n s=rs20250326; t=1777022846; v=1;\n b=pxhTFz/34d+qzWUPkKOAl9qnQxQfGAWOTTRUdWAK/VRv7TzRScTi0MgCJrAp39do\n H8JV77fij5ko3LVHP3tkaoAlXXdAq+bVmu5EpWjuxdm2GT8r8y13qbGnLOKOzKom\n xwp2r4vnixZHM9+rcOQoVJjT3nrfeAux4dOXLyoKzhjSrZRA2cv14jC8rkByb7cJ\n UWN7qidvrY6u5UjtH3uBBbdCL8OPJlHyhkTHLzQV4/2nQFbPIHtIasDtvTgqAAjV\n Hc23WVwZzH75v0LGpki4QyX5OcpT2KWM+hkDLxcJyxyhp6hnswgInBkBGA4NBIpU\n TbZUkQeflPjhNN1PyltV9g==", "From": "Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>", "Subject": "[PATCH v4 0/6] virtio-gpu: Force RCU when unmapping blob", "Date": "Fri, 24 Apr 2026 18:27:05 +0900", "Message-Id": "<20260424-force_rcu-v4-0-feccfaca0568@rsg.ci.i.u-tokyo.ac.jp>", "MIME-Version": "1.0", "Content-Type": "text/plain; charset=\"utf-8\"", "Content-Transfer-Encoding": "7bit", "X-B4-Tracking": "v=1; b=H4sIAAAAAAAC/33M0QrCIBiG4VsZHqf466aro+4jIpzTZsEcWtIYu\n /fcINpJHb4fH8+EognORHQoJhRMctH5Pke5K5DuVH812LW5EaOsAsoktj5ocwn6iQUILUvOJbc\n S5f8QjHWv1Tqdc3cuPnwYVzrBsn6U/UZJgClubC2oEkxKJY4hXol2xJEnfvj76InS5DaghUzsy\n zDgW4ZlBloDWtWlFu1/hn8YQQGqLcMXxtaNVdaWNVQ/mXme3z/6d4c9AQAA", "X-Change-ID": "20251027-force_rcu-616c743373f7", "To": "qemu-devel@nongnu.org, Dmitry Osipenko <dmitry.osipenko@collabora.com>", "Cc": "Paolo Bonzini <pbonzini@redhat.com>,\n \"Michael S. Tsirkin\" <mst@redhat.com>,\n =?utf-8?q?Alex_Benn=C3=A9e?= <alex.bennee@linaro.org>,\n Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>", "X-Mailer": "b4 0.16-dev-16047", "Received-SPF": "pass client-ip=49.212.243.89;\n envelope-from=odaki@rsg.ci.i.u-tokyo.ac.jp; helo=www3579.sakura.ne.jp", "X-Spam_score_int": "-16", "X-Spam_score": "-1.7", "X-Spam_bar": "-", "X-Spam_report": "(-1.7 / 5.0 requ) BAYES_00=-1.9, DKIM_INVALID=0.1,\n DKIM_SIGNED=0.1, SPF_HELO_NONE=0.001,\n SPF_PASS=-0.001 autolearn=no autolearn_force=no", "X-Spam_action": "no action", "X-BeenThere": "qemu-devel@nongnu.org", "X-Mailman-Version": "2.1.29", "Precedence": "list", "List-Id": "qemu development <qemu-devel.nongnu.org>", "List-Unsubscribe": "<https://lists.nongnu.org/mailman/options/qemu-devel>,\n <mailto:qemu-devel-request@nongnu.org?subject=unsubscribe>", "List-Archive": "<https://lists.nongnu.org/archive/html/qemu-devel>", "List-Post": "<mailto:qemu-devel@nongnu.org>", "List-Help": "<mailto:qemu-devel-request@nongnu.org?subject=help>", "List-Subscribe": "<https://lists.nongnu.org/mailman/listinfo/qemu-devel>,\n <mailto:qemu-devel-request@nongnu.org?subject=subscribe>", "Errors-To": "qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org", "Sender": "qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org" }, "content": "Unmapping a blob changes the memory map, which is protected with RCU.\nRCU is designed to minimize the read-side overhead at the cost of\nreclamation delay. While this design usually makes sense, it is\nproblematic when unmapping a blob because the operation blocks all\nvirtio-gpu commands and causes perceivable disruption.\n\nMinimize such the disruption with force_rcu(), which minimizes the\nreclamation delay at the cost of a read-side overhead.\n\nSigned-off-by: Akihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>\n---\nChanges in v4:\n- Keep qemu_event_wait() retrying so it preserves wait-forever\n semantics.\n- Add \"scripts/checkpatch: Avoid false positive on empty blocks\" to\n cover the empty wait loop introduced by\n \"qemu-thread: Add qemu_event_timedwait()\".\n- Link to v3: https://lore.kernel.org/qemu-devel/20260115-force_rcu-v3-0-1f8bfaff4815@rsg.ci.i.u-tokyo.ac.jp\n\nChanges in v3:\n- Fix immediate timeout in qemu_futex_timedwait() for Windows.\n- Dropped patch \"timer: Rename init_clocks() to qemu_clock_init()\".\n- Link to v2: https://lore.kernel.org/qemu-devel/20251213-force_rcu-v2-0-1de1ca84c6d6@rsg.ci.i.u-tokyo.ac.jp\n\nChanges in v2:\n- Stopped overloading the call_rcu1() and force_rcu() notifications onto\n one event. This fixes a deadlock after try_dequeue() caused by\n incorrect masking of call_rcu1() notifications, and eliminates\n spurious force quiescent states caused by being confused with a\n call_rcu1() notification.\n changes the logic significantly.\n- Merged the rcu_call_count and forced variables into one to avoid\n the race between them that used to require a loop to resolve.\n- Aligned the type of the duration variable in qemu_futex_timedwait()\n for Windows.\n- Fixed timespec of qemu_futex_timedwait() for 32-bit Linux.\n- Link to v1: https://lore.kernel.org/qemu-devel/20251029-force_rcu-v1-0-bf860a6277a6@rsg.ci.i.u-tokyo.ac.jp\n\n---\nAkihiko Odaki (6):\n futex: Add qemu_futex_timedwait()\n qemu-thread: Add qemu_event_timedwait()\n rcu: Use call_rcu() in synchronize_rcu()\n rcu: Wake the RCU thread when draining\n virtio-gpu: Force RCU when unmapping blob\n scripts/checkpatch: Avoid false positive on empty blocks\n\n include/qemu/futex.h | 36 +++++++++++++---\n include/qemu/rcu.h | 1 +\n include/qemu/thread-posix.h | 11 +++++\n include/qemu/thread.h | 9 +++-\n hw/display/virtio-gpu-virgl.c | 1 +\n util/event.c | 31 +++++++++++---\n util/qemu-thread-posix.c | 11 +----\n util/rcu.c | 98 ++++++++++++++++++++++++-------------------\n scripts/checkpatch.pl | 3 +-\n 9 files changed, 137 insertions(+), 64 deletions(-)\n---\nbase-commit: 98b060da3a4f92b2a994ead5b16a87e783baf77c\nchange-id: 20251027-force_rcu-616c743373f7\n\nBest regards,\n-- \nAkihiko Odaki <odaki@rsg.ci.i.u-tokyo.ac.jp>" }