From mboxrd@z Thu Jan 1 00:00:00 1970 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 60F1D10ED659 for ; Fri, 27 Mar 2026 11:25:38 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1w65Ji-0002ld-8N; Fri, 27 Mar 2026 07:25:30 -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 1w65JM-0002Wk-Iv for qemu-devel@nongnu.org; Fri, 27 Mar 2026 07:25:10 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1w65JK-0002Y1-2D for qemu-devel@nongnu.org; Fri, 27 Mar 2026 07:25:08 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1774610703; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=FNCT5ZoHgHqOwm6hSuQVycDXB94uRJgvK7uT2R8m9o8=; b=GrK5QXnp10YCuz1RhgHRr9KQBksBh+84y24JBS3RkmxBw7/H8MEk4oKkh5LYMmxLWOdOO3 Ql+Vi+fGLb0nlRVF5JoZbF5f7oSJ21zfCJ5ebZO2DP6NsKbT2WjSJAKNn8oEua2+Vxmuxh zpYbKhf89rbyj6E+zBLOHjoEL7OHLTA= Received: from mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (ec2-54-186-198-63.us-west-2.compute.amazonaws.com [54.186.198.63]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-317-kqBgc_Q_ObOA5yxSaUVCaw-1; Fri, 27 Mar 2026 07:25:00 -0400 X-MC-Unique: kqBgc_Q_ObOA5yxSaUVCaw-1 X-Mimecast-MFC-AGG-ID: kqBgc_Q_ObOA5yxSaUVCaw_1774610698 Received: from mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.17]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-01.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 6CBD019560AE; Fri, 27 Mar 2026 11:24:58 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.45.242.6]) by mx-prod-int-05.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id F2D7F1955D84; Fri, 27 Mar 2026 11:24:57 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id ABAE821E6937; Fri, 27 Mar 2026 12:24:55 +0100 (CET) From: Markus Armbruster To: "Zhang, GuoQing (Sam)" Cc: Samuel Zhang , , , , , , , , , Subject: Re: [PATCH v3] migration/rdma: add x-rdma-chunk-size parameter In-Reply-To: <9b6b3d6a-4f48-4e90-b2fc-7cfcc6c8651d@amd.com> (GuoQing Zhang's message of "Fri, 27 Mar 2026 18:27:07 +0800") References: <20260327065006.2567463-1-guoqing.zhang@amd.com> <87h5q17gh8.fsf@pond.sub.org> <9b6b3d6a-4f48-4e90-b2fc-7cfcc6c8651d@amd.com> Date: Fri, 27 Mar 2026 12:24:55 +0100 Message-ID: <87y0jd5xbs.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain X-Scanned-By: MIMEDefang 3.0 on 10.30.177.17 Received-SPF: pass client-ip=170.10.129.124; envelope-from=armbru@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -20 X-Spam_score: -2.1 X-Spam_bar: -- X-Spam_report: (-2.1 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.001, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H2=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, RCVD_IN_VALIDITY_SAFE_BLOCKED=0.001, SPF_HELO_PASS=-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: qemu development 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 "Zhang, GuoQing (Sam)" writes: > On 2026/3/27 17:45, Markus Armbruster wrote: >> Samuel Zhang writes: >> >>> The default 1MB RDMA chunk size causes slow live migration because >>> each chunk triggers a write_flush (ibv_post_send). For 8GB RAM, >>> 1MB chunk size produces ~15000 flushes vs ~3700 with 1024MB chunk size. >>> >>> Add x-rdma-chunk-size parameter to configure the RDMA chunk size for >>> faster migration. >>> Usage: `migrate_set_parameter x-rdma-chunk-size 1024M` >>> >>> Performance with RDMA live migration of 8GB RAM VM: >>> >>> | x-rdma-chunk-size (B) | time (s) | throughput (MB/s) | >>> |-----------------------|----------|-------------------| >>> | 1M (default) | 37.915 | 1,007 | >>> | 32M | 17.880 | 2,260 | >>> | 1024M | 4.368 | 17,529 | >>> >>> Signed-off-by: Samuel Zhang [...] >>> diff --git a/qapi/migration.json b/qapi/migration.json >>> index 7134d4ce47..292d96c95a 100644 >>> --- a/qapi/migration.json >>> +++ b/qapi/migration.json >>> @@ -806,7 +806,7 @@ >>> # >>> # Features: >>> # >>> -# @unstable: Members @x-checkpoint-delay and >>> +# @unstable: Members @x-checkpoint-delay, @x-rdma-chunk-size, and >>> # @x-vcpu-dirty-limit-period are experimental. >>> # >>> # Since: 2.4 >>> @@ -831,6 +831,7 @@ >>> 'mode', >>> 'zero-page-detection', >>> 'direct-io', >>> + { 'name': 'x-rdma-chunk-size', 'features': [ 'unstable' ] }, >>> 'cpr-exec-command'] } >>> >>> ## >>> @@ -1007,9 +1008,14 @@ >>> # is @cpr-exec. The first list element is the program's filename, >>> # the remainder its arguments. (Since 10.2) >>> # >>> +# @x-rdma-chunk-size: RDMA memory registration chunk size in bytes. >>> +# Default is 1MiB. Must be a power of 2 in the range >>> +# [1MiB, 1024MiB]. Only takes effect for RDMA migration. >> >> I believe it applies to channels whose migration address type is is >> "rdma". In MigrationChannel syntax >> >> {"channel-type": ..., "addr": {"transport": "rdma", ...}} >> >> Correct? > > > Correct! Is it OK to update the doc to the following one? Thank you! > > `Only takes effect when migration address transport is "rdma".` The phrasing in the patch feels okay as is. Perhaps "Only applies when migrating via RDMA" to more closely match the description of MigrationAddressType @rdma: Migrate via RDMA. Either way, QAPI schema Acked-by: Markus Armbruster >>> +# (Since 11.1) >>> +# >>> # Features: >>> # >>> -# @unstable: Members @x-checkpoint-delay and >>> +# @unstable: Members @x-checkpoint-delay, @x-rdma-chunk-size, and >>> # @x-vcpu-dirty-limit-period are experimental. >>> # >>> # Since: 2.4 >>> @@ -1046,6 +1052,8 @@ >>> '*mode': 'MigMode', >>> '*zero-page-detection': 'ZeroPageDetection', >>> '*direct-io': 'bool', >>> + '*x-rdma-chunk-size': { 'type': 'uint64', >>> + 'features': [ 'unstable' ] }, >>> '*cpr-exec-command': [ 'str' ]} } >> >>> ##