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 E6C8DC433EF for ; Mon, 4 Jul 2022 12:28:13 +0000 (UTC) Received: from localhost ([::1]:37752 helo=lists1p.gnu.org) by lists.gnu.org with esmtp (Exim 4.90_1) (envelope-from ) id 1o8LBV-0000NP-1g for qemu-devel@archiver.kernel.org; Mon, 04 Jul 2022 08:28:13 -0400 Received: from eggs.gnu.org ([2001:470:142:3::10]:49836) by lists.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1o8L0D-00039t-5R for qemu-devel@nongnu.org; Mon, 04 Jul 2022 08:16:33 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:23556) by eggs.gnu.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.90_1) (envelope-from ) id 1o8L05-00081Q-RH for qemu-devel@nongnu.org; Mon, 04 Jul 2022 08:16:30 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1656936985; h=from:from:reply-to: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=aOJCqS7UfWWzoRmXKF4POPT3Ix3gXK6plRtCN+7uK+0=; b=Cxw3mVgwAOcVIj8hghliBLMVitCT0brqTF32h01mHsag2guzcNeNV0dgBxrESMAZrC/jZh rpG/q7cgCS/WSfHRwRQBcy0bbXXZH1SdkX4Q867Qv9xPpLMdbiSKHKKhaCQfQj8bTHczd0 SIGZ0aNPjanqXOvH5IYKR+D/1O/ihjE= 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-120-_ydnflfONJqXyqsuTFLrTg-1; Mon, 04 Jul 2022 08:16:23 -0400 X-MC-Unique: _ydnflfONJqXyqsuTFLrTg-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id 77B32801E95 for ; Mon, 4 Jul 2022 12:16:23 +0000 (UTC) Received: from redhat.com (unknown [10.33.36.151]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 7364A41617E; Mon, 4 Jul 2022 12:16:21 +0000 (UTC) Date: Mon, 4 Jul 2022 13:16:17 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Markus Armbruster Cc: "Dr. David Alan Gilbert" , Leonardo Bras , Juan Quintela , Eric Blake , Peter Xu , qemu-devel@nongnu.org Subject: Re: [PATCH v2 2/3] Add zero-copy-copied migration stat Message-ID: References: <20220701155935.482503-1-leobras@redhat.com> <20220701155935.482503-3-leobras@redhat.com> <877d4tz9gx.fsf@pond.sub.org> <87k08tw0bq.fsf@pond.sub.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <87k08tw0bq.fsf@pond.sub.org> User-Agent: Mutt/2.2.6 (2022-06-05) X-Scanned-By: MIMEDefang 2.85 on 10.11.54.10 Received-SPF: pass client-ip=170.10.133.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -16 X-Spam_score: -1.7 X-Spam_bar: - X-Spam_report: (-1.7 / 5.0 requ) BAYES_00=-1.9, DKIM_INVALID=0.1, DKIM_SIGNED=0.1, RCVD_IN_DNSWL_NONE=-0.0001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001, T_SCC_BODY_TEXT_LINE=-0.01 autolearn=no 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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Mon, Jul 04, 2022 at 02:04:41PM +0200, Markus Armbruster wrote: > "Dr. David Alan Gilbert" writes: > > > * Daniel P. Berrangé (berrange@redhat.com) wrote: > >> On Mon, Jul 04, 2022 at 08:18:54AM +0200, Markus Armbruster wrote: > >> > Leonardo Bras writes: > >> > > >> > > 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 phase > >> > > # (since 7.0). > >> > > # > >> > > +# @zero-copy-copied: The number of zero-copy flushes that reported data sent > >> > > +# using zero-copy that ended up being copied. (since 7.2) > > since 7.1, unless you're planning for really tortuous review :) > > >> > > >> > 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? > >> > >> MigrationCapability field @zero-copy-send instructs QEMU to try to > >> avoid copying data between userspace and kernel space when transmitting > >> RAM region. > >> > >> Even if the kernel supports zero copy, it is not guaranteed to happen, > >> it is merely a request to try. > >> > >> QEMU periodically (once per migration iteration) flushes outstanding > >> zero-copy requests and gets an indication back of whether any copies > >> took place or not. > >> > >> So this counter is a reflection of how many iterations resulted in > >> zero-copy not being fully honoured. > >> > >> 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. > >> > >> 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) Any one have preferences on the name - i get slight put off by the repeated word in the property name here. @zero-copy-rejects ? @zero-copy-misses ? @zero-copy-fails ? With regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|