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 C8E84C43334 for ; Mon, 4 Jul 2022 12:06:29 +0000 (UTC) Received: from localhost ([::1]:51494 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1o8KqS-0005r0-HQ for qemu-devel@archiver.kernel.org; Mon, 04 Jul 2022 08:06:28 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:46714) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1o8Kp6-0004LQ-Hl for qemu-devel@nongnu.org; Mon, 04 Jul 2022 08:05:06 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.129.124]:21481) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1o8Kop-0005aZ-9C for qemu-devel@nongnu.org; Mon, 04 Jul 2022 08:05:03 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1656936286; 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: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=idSr6dw4yRLQXaxU5k8jjz6d+spG3QK0xjsXOmwVGBc=; b=ZCwgHZeFtInSKGCjGQxTPZfvlZCQodkpWJ6llPcSI3A6eo4nBgEMPOgTXBmKrduATygSEd yfJPIsvC9tjLBzfFMv8PvXIVu0UXMzFSvHkcknBrQAsRGcnHmDyharYNxLFoAGKioMeMxv AG93dbCpYtvxTud5SLzMvGSPDEILrkU= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-367-YTDlv_5HMTaamwmmxKXkGQ-1; Mon, 04 Jul 2022 08:04:44 -0400 X-MC-Unique: YTDlv_5HMTaamwmmxKXkGQ-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.rdu2.redhat.com [10.11.54.4]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 4A76185A582 for ; Mon, 4 Jul 2022 12:04:43 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.195.112]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 183FA2026D64; Mon, 4 Jul 2022 12:04:43 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id C4A0821E690D; Mon, 4 Jul 2022 14:04:41 +0200 (CEST) From: Markus Armbruster To: "Dr. David Alan Gilbert" Cc: Daniel P. =?utf-8?Q?Berrang=C3=A9?= , Leonardo Bras , Juan Quintela , Eric Blake , Peter Xu , qemu-devel@nongnu.org Subject: Re: [PATCH v2 2/3] Add zero-copy-copied migration stat References: <20220701155935.482503-1-leobras@redhat.com> <20220701155935.482503-3-leobras@redhat.com> <877d4tz9gx.fsf@pond.sub.org> Date: Mon, 04 Jul 2022 14:04:41 +0200 In-Reply-To: (David Alan Gilbert's message of "Mon, 4 Jul 2022 12:40:09 +0100") Message-ID: <87k08tw0bq.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/27.2 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 2.78 on 10.11.54.4 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: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.082, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 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" "Dr. David Alan Gilbert" writes: > * Daniel P. Berrang=C3=A9 (berrange@redhat.com) wrote: >> On Mon, Jul 04, 2022 at 08:18:54AM +0200, Markus Armbruster wrote: >> > Leonardo Bras writes: >> >=20 >> > > Signed-off-by: Leonardo Bras >> > > --- >> > > qapi/migration.json | 5 ++++- >> > > migration/migration.c | 1 + >> > > monitor/hmp-cmds.c | 4 ++++ >> > > 3 files changed, 9 insertions(+), 1 deletion(-) >> > > >> > > diff --git a/qapi/migration.json b/qapi/migration.json >> > > index 7102e474a6..925f009868 100644 >> > > --- a/qapi/migration.json >> > > +++ b/qapi/migration.json >> > > @@ -55,6 +55,9 @@ >> > > # @postcopy-bytes: The number of bytes sent during the post-copy ph= ase >> > > # (since 7.0). >> > > # >> > > +# @zero-copy-copied: The number of zero-copy flushes that reported = data sent >> > > +# using zero-copy that ended up being copied. (s= ince 7.2) since 7.1, unless you're planning for really tortuous review :) >> >=20 >> > The description feels awkward. What's a "zero-copy flush", and why >> > should the user care? I figure what users care about is the number of >> > all-zero pages we had to "copy", i.e. send the bulky way. Is this what >> > @zero-copy-copied reports? >>=20 >> MigrationCapability field @zero-copy-send instructs QEMU to try to >> avoid copying data between userspace and kernel space when transmitting >> RAM region. >>=20 >> Even if the kernel supports zero copy, it is not guaranteed to happen, >> it is merely a request to try. >>=20 >> QEMU periodically (once per migration iteration) flushes outstanding >> zero-copy requests and gets an indication back of whether any copies >> took place or not. >>=20 >> So this counter is a reflection of how many iterations resulted in >> zero-copy not being fully honoured. >>=20 >> IOW, ideally this counter will always be zero. If it is non-zero, >> then the magnitude gives a very very very rough guide to what's >> going on. If it is '1' then it was just a transient limitation. >> If it matches the number of migration iterations, then it is a >> more systemic limitation. >>=20 >> Incidentally, do we report the migration iteration count ? I >> thought we did, but i'm not finding it now that I look. > > Yes we do; it's dirty-sync-count Please rephrase the documentation of @zero-copy-copied in terms of @dirty-sync-count. Here's my attempt. # @zero-copy-copied: Number of times dirty RAM synchronization could not # avoid copying zero pages. This is between 0 and # @dirty-sync-count. (since 7.1)