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 E0E8A10ED642 for ; Fri, 27 Mar 2026 09:46:57 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1w63la-0008J9-A4; Fri, 27 Mar 2026 05:46:10 -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 1w63lY-0008J0-Qf for qemu-devel@nongnu.org; Fri, 27 Mar 2026 05:46:08 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1w63lV-0000DH-DT for qemu-devel@nongnu.org; Fri, 27 Mar 2026 05:46:08 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1774604763; 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=mGDcydiPhcLwqmBnOCVBl+fyApkhm1WxMV8TW3ou7ag=; b=a4kkjB7lI1sAuNTfs58D6SfBP0d6ioq0BqpRJJSVHLoj/a5WxqnAF8EA65SEJ3D4kEwTNq j3ttHNcaW5FkAssuQCMGZ6mw9W7z51XAC6Melm4g42BpDxKe8OHSwEnWJQP+YFTA1TTaBO 3zDi3kG36GOaiOq93k9q3OHVNIiakLc= Received: from mx-prod-mc-03.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-392-vil8qoCjMUC7WotswSxJLQ-1; Fri, 27 Mar 2026 05:46:00 -0400 X-MC-Unique: vil8qoCjMUC7WotswSxJLQ-1 X-Mimecast-MFC-AGG-ID: vil8qoCjMUC7WotswSxJLQ_1774604758 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-03.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 8FE901956062; Fri, 27 Mar 2026 09:45:58 +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 23EB41955D71; Fri, 27 Mar 2026 09:45:58 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id CF79A21E6937; Fri, 27 Mar 2026 10:45:55 +0100 (CET) From: Markus Armbruster To: Samuel Zhang Cc: , , , , , , , , Subject: Re: [PATCH v3] migration/rdma: add x-rdma-chunk-size parameter In-Reply-To: <20260327065006.2567463-1-guoqing.zhang@amd.com> (Samuel Zhang's message of "Fri, 27 Mar 2026 14:50:06 +0800") References: <20260327065006.2567463-1-guoqing.zhang@amd.com> Date: Fri, 27 Mar 2026 10:45:55 +0100 Message-ID: <87h5q17gh8.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=170.10.133.124; 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 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/migration/options.c b/migration/options.c > index f33b297929..bc61c8665d 100644 > --- a/migration/options.c > +++ b/migration/options.c > @@ -13,6 +13,7 @@ > > #include "qemu/osdep.h" > #include "qemu/error-report.h" > +#include "qemu/units.h" > #include "exec/target_page.h" > #include "qapi/clone-visitor.h" > #include "qapi/error.h" > @@ -90,6 +91,7 @@ const PropertyInfo qdev_prop_StrOrNull; > > #define DEFAULT_MIGRATE_VCPU_DIRTY_LIMIT_PERIOD 1000 /* milliseconds */ > #define DEFAULT_MIGRATE_VCPU_DIRTY_LIMIT 1 /* MB/s */ > +#define DEFAULT_MIGRATE_X_RDMA_CHUNK_SIZE MiB /* 1MB */ The comment is now superfluous. > > const Property migration_properties[] = { > DEFINE_PROP_BOOL("store-global-state", MigrationState, [...] > 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? > +# (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' ]} } > > ##