From patchwork Tue Apr 16 14:42:39 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: "Maciej S. Szmigiero" X-Patchwork-Id: 13631973 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from lists.gnu.org (lists.gnu.org [209.51.188.17]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 220A2C04FF9 for ; Tue, 16 Apr 2024 14:44:38 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rwk2D-0004tO-S5; Tue, 16 Apr 2024 10:43:45 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rwk2B-0004sU-RA for qemu-devel@nongnu.org; Tue, 16 Apr 2024 10:43:43 -0400 Received: from vps-vb.mhejs.net ([37.28.154.113]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1rwk27-0001yS-05 for qemu-devel@nongnu.org; Tue, 16 Apr 2024 10:43:43 -0400 Received: from MUA by vps-vb.mhejs.net with esmtps (TLS1.2) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1rwk1h-0002cY-Ey; Tue, 16 Apr 2024 16:43:13 +0200 From: "Maciej S. Szmigiero" To: Peter Xu , Fabiano Rosas Cc: Alex Williamson , =?utf-8?q?C=C3=A9dric_Le_G?= =?utf-8?q?oater?= , Eric Blake , Markus Armbruster , Avihai Horon , Joao Martins , qemu-devel@nongnu.org Subject: =?utf-8?q?=5BPATCH_RFC_00/26=5D_Multifd_=F0=9F=94=80_device_state_t?= =?utf-8?q?ransfer_support_with_VFIO_consumer?= Date: Tue, 16 Apr 2024 16:42:39 +0200 Message-ID: X-Mailer: git-send-email 2.44.0 MIME-Version: 1.0 Received-SPF: pass client-ip=37.28.154.113; envelope-from=mail@maciej.szmigiero.name; helo=vps-vb.mhejs.net X-Spam_score_int: -18 X-Spam_score: -1.9 X-Spam_bar: - X-Spam_report: (-1.9 / 5.0 requ) BAYES_00=-1.9, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org From: "Maciej S. Szmigiero" VFIO device state transfer is currently done via the main migration channel. This means that transfers from multiple VFIO devices are done sequentially and via just a single common migration channel. Such way of transferring VFIO device state migration data reduces performance and severally impacts the migration downtime (~50%) for VMs that have multiple such devices with large state size - see the test results below. However, we already have a way to transfer migration data using multiple connections - that's what multifd channels are. Unfortunately, multifd channels are currently utilized for RAM transfer only. This patch set adds a new framework allowing their use for device state transfer too. The wire protocol is based on Avihai's x-channel-header patches, which introduce a header for migration channels that allow the migration source to explicitly indicate the migration channel type without having the target deduce the channel type by peeking in the channel's content. The new wire protocol can be switch on and off via migration.x-channel-header option for compatibility with older QEMU versions and testing. Switching the new wire protocol off also disables device state transfer via multifd channels. The device state transfer can happen either via the same multifd channels as RAM data is transferred, mixed with RAM data (when migration.x-multifd-channels-device-state is 0) or exclusively via dedicated device state transfer channels (when migration.x-multifd-channels-device-state > 0). Using dedicated device state transfer multifd channels brings further performance benefits since these channels don't need to participate in the RAM sync process. These patches introduce a few new SaveVMHandlers: * "save_live_complete_precopy_async{,wait}" handlers that allow device to provide its own asynchronous transmission of the remaining data at the end of a precopy phase. The "save_live_complete_precopy_async" handler is supposed to start such transmission (for example, by launching appropriate threads) while the "save_live_complete_precopy_async_wait" handler is supposed to wait until such transfer has finished (for example, until the sending threads have exited). * "load_state_buffer" and its caller qemu_loadvm_load_state_buffer() that allow providing device state buffer to explicitly specified device via its idstr and instance id. * "load_finish" the allows migration code to poll whether a device-specific asynchronous device state loading operation had finished before proceeding further in the migration process (with associated condition variable for notification to avoid unnecessary polling). A VFIO device migration consumer for the new multifd channels device state migration framework was implemented with a reassembly process for the multifd received data since device state packets sent via different multifd channels can arrive out-of-order. The VFIO device data loading process happens in a separate thread in order to avoid blocking a multifd receive thread during this fairly long process. Test setup: Source machine: 2x Xeon Gold 5218 / 192 GiB RAM Mellanox ConnectX-7 with 100GbE link 6.9.0-rc1+ kernel Target machine: 2x Xeon Platinum 8260 / 376 GiB RAM Mellanox ConnectX-7 with 100GbE link 6.6.0+ kernel VM: CPU 12cores x 2threads / 15 GiB RAM / 4x Mellanox ConnectX-7 VF Migration config: 15 multifd channels total new way had 4 channels dedicated to device state transfer x-return-path=true, x-switchover-ack=true Downtime with ~400 MiB VFIO total device state size: TLS off TLS on migration.x-channel-header=false (old way) ~2100 ms ~2300 ms migration.x-channel-header=true (new way) ~1100 ms ~1200 ms IMPROVEMENT ~50% ~50% This patch set is also available as a git tree: https://github.com/maciejsszmigiero/qemu/tree/multifd-device-state-transfer-vfio Avihai Horon (7): migration: Add x-channel-header pseudo-capability migration: Add migration channel header send/receive migration: Add send/receive header for main channel migration: Allow passing migration header in migration channel creation migration: Add send/receive header for postcopy preempt channel migration: Add send/receive header for multifd channel migration: Enable x-channel-header pseudo-capability Maciej S. Szmigiero (19): multifd: change multifd_new_send_channel_create() param type migration: Add a DestroyNotify parameter to socket_send_channel_create() multifd: pass MFDSendChannelConnectData when connecting sending socket migration/postcopy: pass PostcopyPChannelConnectData when connecting sending preempt socket migration/options: Mapped-ram is not channel header compatible vfio/migration: Add save_{iterate,complete_precopy}_started trace events migration/ram: Add load start trace event migration/multifd: Zero p->flags before starting filling a packet migration: Add save_live_complete_precopy_async{,wait} handlers migration: Add qemu_loadvm_load_state_buffer() and its handler migration: Add load_finish handler and associated functions migration: Add x-multifd-channels-device-state parameter migration: Add MULTIFD_DEVICE_STATE migration channel type migration/multifd: Device state transfer support - receive side migration/multifd: Convert multifd_send_pages::next_channel to atomic migration/multifd: Device state transfer support - send side migration/multifd: Add migration_has_device_state_support() vfio/migration: Multifd device state transfer support - receive side vfio/migration: Multifd device state transfer support - send side hw/core/machine.c | 1 + hw/vfio/migration.c | 530 ++++++++++++++++++++++++++++++++- hw/vfio/trace-events | 15 +- include/hw/vfio/vfio-common.h | 25 ++ include/migration/misc.h | 5 + include/migration/register.h | 67 +++++ migration/channel.c | 68 +++++ migration/channel.h | 17 ++ migration/file.c | 5 +- migration/migration-hmp-cmds.c | 7 + migration/migration.c | 110 ++++++- migration/migration.h | 6 + migration/multifd-zlib.c | 2 +- migration/multifd-zstd.c | 2 +- migration/multifd.c | 512 ++++++++++++++++++++++++++----- migration/multifd.h | 62 +++- migration/options.c | 66 ++++ migration/options.h | 2 + migration/postcopy-ram.c | 81 ++++- migration/ram.c | 1 + migration/savevm.c | 112 +++++++ migration/savevm.h | 7 + migration/socket.c | 6 +- migration/socket.h | 3 +- migration/trace-events | 3 + qapi/migration.json | 16 +- 26 files changed, 1626 insertions(+), 105 deletions(-)