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Tue, 5 Jul 2022 16:52:54 +0000 (UTC) Received: from redhat.com (unknown [10.33.36.72]) by smtp.corp.redhat.com (Postfix) with ESMTPS id 0524640336E; Tue, 5 Jul 2022 16:52:52 +0000 (UTC) Date: Tue, 5 Jul 2022 17:52:50 +0100 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= To: Juan Quintela Cc: "Dr. David Alan Gilbert" , qemu-devel@nongnu.org, Leonardo Bras , Philippe =?utf-8?Q?Mathieu-Daud=C3=A9?= , Marcel Apfelbaum , Eduardo Habkost , Yanan Wang Subject: Re: [PATCH 5/5] multifd: Only sync once each full round of memory Message-ID: References: <20220621140507.1246-1-quintela@redhat.com> <20220621140507.1246-6-quintela@redhat.com> <8735ff1tn1.fsf@secure.mitica> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <8735ff1tn1.fsf@secure.mitica> 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=170.10.129.124; envelope-from=berrange@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -28 X-Spam_score: -2.9 X-Spam_bar: -- X-Spam_report: (-2.9 / 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, RCVD_IN_DNSWL_LOW=-0.7, 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: , Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: "Qemu-devel" On Tue, Jul 05, 2022 at 05:11:46PM +0200, Juan Quintela wrote: > "Dr. David Alan Gilbert" wrote: > > * Juan Quintela (quintela@redhat.com) wrote: > >> We need to add a new flag to mean to sync at that point. > >> Notice that we still synchronize at the end of setup and at the end of > >> complete stages. > >> > >> Signed-off-by: Juan Quintela > >> --- > >> migration/migration.c | 2 +- > >> migration/ram.c | 42 ++++++++++++++++++++++++++++++------------ > >> 2 files changed, 31 insertions(+), 13 deletions(-) > >> > >> diff --git a/migration/migration.c b/migration/migration.c > >> index 3f79df0b70..6627787fc2 100644 > >> --- a/migration/migration.c > >> +++ b/migration/migration.c > >> @@ -4283,7 +4283,7 @@ static Property migration_properties[] = { > >> DEFAULT_MIGRATE_ANNOUNCE_STEP), > >> /* We will change to false when we introduce the new mechanism */ > >> DEFINE_PROP_BOOL("multifd-sync-each-iteration", MigrationState, > >> - multifd_sync_each_iteration, true), > >> + multifd_sync_each_iteration, false), > >> > >> /* Migration capabilities */ > >> DEFINE_PROP_MIG_CAP("x-xbzrle", MIGRATION_CAPABILITY_XBZRLE), > >> diff --git a/migration/ram.c b/migration/ram.c > >> index 2c7289edad..6792986565 100644 > >> --- a/migration/ram.c > >> +++ b/migration/ram.c > >> @@ -81,6 +81,7 @@ > >> #define RAM_SAVE_FLAG_XBZRLE 0x40 > >> /* 0x80 is reserved in migration.h start with 0x100 next */ > >> #define RAM_SAVE_FLAG_COMPRESS_PAGE 0x100 > >> +#define RAM_SAVE_FLAG_MULTIFD_SYNC 0x200 > > > > Note this is the very last usable flag! > > We can recover two flags right now: > > RAM_SAVE_FLAG_FULL is not used anymore. > 0x80 is free since years ago. > > Once multifd is default, there are some other that could go. Non-multifd migration isn't likely to go away any time soon, given distros desire to support migration between QEMU's with quite significantly different versions. So feels like quite a long time before we might reclaim more flags. > > We could do with avoiding using them as flags where we dont need to. > > I can't really think on another way to do it. The other thing that I > can do is just reuse one of the flags that don't make sense for multifd > (RAM_SAVE_FLAG_ZERO after zero pages patch, > RAM_SAVE_FLAG_XBZRLE/COMPRESS_PAGE). Re-using flags based on use context differences feels like a recipe to confuse people. 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 :|