From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:52810) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1f3F9l-0004FN-H4 for qemu-devel@nongnu.org; Tue, 03 Apr 2018 02:10:58 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1f3F9h-0000E9-H9 for qemu-devel@nongnu.org; Tue, 03 Apr 2018 02:10:57 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:49514 helo=mx1.redhat.com) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1f3F9h-0000Dy-Bq for qemu-devel@nongnu.org; Tue, 03 Apr 2018 02:10:53 -0400 Date: Tue, 3 Apr 2018 14:10:40 +0800 From: Peter Xu Message-ID: <20180403061040.GD26441@xz-mi> References: <20180331185536.4835-1-bala24@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20180331185536.4835-1-bala24@linux.vnet.ibm.com> Subject: Re: [Qemu-devel] [PATCH] migration: calculate expected_downtime with ram_bytes_remaining() List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Balamuruhan S Cc: qemu-devel@nongnu.org, amit.shah@redhat.com, quintela@redhat.com On Sun, Apr 01, 2018 at 12:25:36AM +0530, Balamuruhan S wrote: > expected_downtime value is not accurate with dirty_pages_rate * page_size, > using ram_bytes_remaining would yeild it correct. > > Signed-off-by: Balamuruhan S > --- > migration/migration.c | 3 +-- > 1 file changed, 1 insertion(+), 2 deletions(-) > > diff --git a/migration/migration.c b/migration/migration.c > index 58bd382730..4e43dc4f92 100644 > --- a/migration/migration.c > +++ b/migration/migration.c > @@ -2245,8 +2245,7 @@ static void migration_update_counters(MigrationState *s, > * recalculate. 10000 is a small enough number for our purposes > */ > if (ram_counters.dirty_pages_rate && transferred > 10000) { > - s->expected_downtime = ram_counters.dirty_pages_rate * > - qemu_target_page_size() / bandwidth; > + s->expected_downtime = ram_bytes_remaining() / bandwidth; This field was removed in e4ed1541ac ("savevm: New save live migration method: pending", 2012-12-20), in which remaing RAM was used. And it was added back in 90f8ae724a ("migration: calculate expected_downtime", 2013-02-22), in which dirty rate was used. However I didn't find a clue on why we changed from using remaining RAM to using dirty rate... So I'll leave this question to Juan. Besides, I'm a bit confused on when we'll want such a value. AFAIU precopy is mostly used by setting up the target downtime before hand, so we should already know the downtime before hand. Then why we want to observe such a thing? Thanks, -- Peter Xu