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 CDF51C5475B for ; Fri, 1 Mar 2024 05:54:11 +0000 (UTC) Received: from localhost ([::1] helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1rfvq4-0003yd-PR; Fri, 01 Mar 2024 00:53:44 -0500 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 1rfvq3-0003yL-9x for qemu-devel@nongnu.org; Fri, 01 Mar 2024 00:53:43 -0500 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 1rfvq1-0007qk-GY for qemu-devel@nongnu.org; Fri, 01 Mar 2024 00:53:43 -0500 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1709272420; 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=wyRkmVMN5nuPIt2PJKAIL4i+J+M7XXVZtG2toE45VXE=; b=Y8o8YQ0Z9D+NsZVfdE3e0zkXOqUlG077kx30GuLI6mp1cOlrOO6fOgO+OmCs4gp9G3JIWy /aB+U6YrXVxH9ngVX/87MzwJ9KQ2R+b6K5W14sVdhtymQ4CL+qkntwh5+WuMSKwswamC2k k5GEPzkotZEiO5B25/lyvZPkMcK7GNI= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.3, cipher=TLS_AES_256_GCM_SHA384) id us-mta-237-qpSv13ZCOHSqKbdM4cZ0Xw-1; Fri, 01 Mar 2024 00:53:35 -0500 X-MC-Unique: qpSv13ZCOHSqKbdM4cZ0Xw-1 Received: from smtp.corp.redhat.com (int-mx06.intmail.prod.int.rdu2.redhat.com [10.11.54.6]) (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 mimecast-mx02.redhat.com (Postfix) with ESMTPS id CC601841861; Fri, 1 Mar 2024 05:53:34 +0000 (UTC) Received: from blackfin.pond.sub.org (unknown [10.39.193.4]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 4A21D2166B33; Fri, 1 Mar 2024 05:53:34 +0000 (UTC) Received: by blackfin.pond.sub.org (Postfix, from userid 1000) id 0B3E221E6743; Fri, 1 Mar 2024 06:53:33 +0100 (CET) From: Markus Armbruster To: Hao Xiang Cc: pbonzini@redhat.com, berrange@redhat.com, eduardo@habkost.net, peterx@redhat.com, farosas@suse.de, eblake@redhat.com, thuth@redhat.com, lvivier@redhat.com, jdenemar@redhat.com, marcel.apfelbaum@gmail.com, philmd@linaro.org, wangyanan55@huawei.com, qemu-devel@nongnu.org Subject: Re: [External] Re: [PATCH v3 6/7] migration/multifd: Add zero pages and zero bytes counter to migration status interface. In-Reply-To: (Hao Xiang's message of "Thu, 29 Feb 2024 17:18:33 -0800") References: <20240226195654.934709-1-hao.xiang@bytedance.com> <20240226195654.934709-7-hao.xiang@bytedance.com> <87wmqozzjn.fsf@pond.sub.org> <875xy7u7vb.fsf@pond.sub.org> Date: Fri, 01 Mar 2024 06:53:33 +0100 Message-ID: <87il26sdk2.fsf@pond.sub.org> User-Agent: Gnus/5.13 (Gnus v5.13) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.11.54.6 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=-0.096, 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, 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-bounces+qemu-devel=archiver.kernel.org@nongnu.org Hao Xiang writes: > On Wed, Feb 28, 2024 at 10:01=E2=80=AFPM Markus Armbruster wrote: >> >> Hao Xiang writes: >> >> > On Wed, Feb 28, 2024 at 1:52=E2=80=AFAM Markus Armbruster wrote: >> >> >> >> Hao Xiang writes: >> >> >> >> > This change extends the MigrationStatus interface to track zero pag= es >> >> > and zero bytes counter. >> >> > >> >> > Signed-off-by: Hao Xiang >> >> >> >> [...] >> >> >> >> > diff --git a/qapi/migration.json b/qapi/migration.json >> >> > index a0a85a0312..171734c07e 100644 >> >> > --- a/qapi/migration.json >> >> > +++ b/qapi/migration.json >> >> > @@ -63,6 +63,10 @@ >> >> > # between 0 and @dirty-sync-count * @multifd-channels. (since >> >> > # 7.1) >> >> > # >> >> > +# @zero-pages: number of zero pages (since 9.0) >> >> > +# >> >> > +# @zero-bytes: number of zero bytes sent (since 9.0) >> >> > +# >> >> >> >> Awfully terse. How are these two related? >> > >> > Sorry I forgot to address the same feedback from the last version. >> >> Happens :) >> >> > zero-pages are the number of pages being detected as all "zero" and >> > hence the payload isn't sent over the network. zero-bytes is basically >> > zero-pages * page_size. It's the number of bytes migrated (but not >> > actually sent through the network) because they are all "zero". These >> > two are related to the existing interface below. normal and >> > normal-bytes are the same representation of pages who are not all >> > "zero" and are actually sent through the network. >> > >> > # @normal: number of normal pages (since 1.2) >> > # >> > # @normal-bytes: number of normal bytes sent (since 1.2) >> >> We also have >> >> # @duplicate: number of duplicate (zero) pages (since 1.2) >> # >> # @skipped: number of skipped zero pages. Always zero, only provided f= or >> # compatibility (since 1.5) >> >> Page skipping was introduced in 1.5, and withdrawn in 1.5.3 and 1.6. >> @skipped was formally deprecated in 8.1. It'll soon be gone, no need to >> worry about it now. >> >> That leaves three values related to pages sent: @normal (and >> @normal-bytes), @duplicate (but no @duplicate-bytes), and @zero-pages >> (and @zero-bytes). >> >> I unwittingly created a naming inconsistency between @normal, >> @duplicate, and @zero-pages when I asked you to rename @zero to >> @zero-pages. >> >> The meaning of the three values is not obvious, and the doc comments >> don't explain them. Can you, or anybody familiar with migration, >> explain them to me? >> >> MigrationStats return some values as bytes, some as pages, and some as >> both. I hate that. Can we standardize on bytes? > > I added zero/zero-bytes because I thought they were not there. But it > turns out "duplicate" is for that purpose. "zero/zero-bytes" is really > additional information to "normal/normal-bytes". Peter suggested that > if we add "zero/zero-bytes" we can slowly retire "duplicate" at a > later point. "zero" is a better name than "duplicate". Identical non-zero pages are possible, and they are duplicates, too. If you add @zero with the intent to replace @duplicate, you should immediately deprecate @duplicate. If you need assistance with that, just ask. > I don't know the historical reason why pages/bytes are used the way it > is today. The way I understand migration, the granularity of ram > migration is "page". There are only two types of pages 1) normal 2) > zero. Zero pages' playload are not sent through the network because we > already know what it looks like. Only the page offset is sent. Normal > pages are pages that are not zero. The entire page is sent through the > network to the target host. This is not at all clear from the documentation of MigrationStats. I think the documentation needs improvement there. > if a user knows the zero/normal count, > they can already calculate the zero-bytes/normal-bytes (zero/normal * > page size) Yes, because member @page-size tells them the multiplier. > but it's just convenient to see both. During development, I > check on these counters a lot and they are useful. QMP is for machines. Machines don't need or want the same quantity in two units. Providing them both bytes and pages is a design mistake. Whether it's worth correcting now is of course debatable. Regardless, the fact @normal-bytes =3D @normal * @page-size needs to be documented. We have # @page-size: The number of bytes per page for the various page-based # statistics (since 2.10) The fact that I inquired how zero-pages and zero-bytes are related might indicate that this isn't quite clear enough. [...]