From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:40693) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1grj0B-0008U7-03 for qemu-devel@nongnu.org; Thu, 07 Feb 2019 07:42:00 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1grj0A-0003xf-0c for qemu-devel@nongnu.org; Thu, 07 Feb 2019 07:41:58 -0500 Received: from mx1.redhat.com ([209.132.183.28]:51624) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1grj09-0003wU-Q0 for qemu-devel@nongnu.org; Thu, 07 Feb 2019 07:41:57 -0500 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 5DAE788E65 for ; Thu, 7 Feb 2019 12:41:55 +0000 (UTC) Date: Thu, 7 Feb 2019 12:41:34 +0000 From: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= Message-ID: <20190207124134.GH19438@redhat.com> Reply-To: Daniel =?utf-8?B?UC4gQmVycmFuZ8Op?= References: <20190206132331.1694-1-quintela@redhat.com> <20190206132331.1694-2-quintela@redhat.com> <20190207113312.GD19438@redhat.com> <877eebg5j4.fsf@trasno.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <877eebg5j4.fsf@trasno.org> Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH 1/4] multifd: Change page count default to 128 List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Juan Quintela Cc: qemu-devel@nongnu.org, Laurent Vivier , Thomas Huth , Markus Armbruster , "Dr. David Alan Gilbert" , Paolo Bonzini On Thu, Feb 07, 2019 at 01:13:51PM +0100, Juan Quintela wrote: > Daniel P. Berrang=C3=A9 wrote: > > On Wed, Feb 06, 2019 at 02:23:28PM +0100, Juan Quintela wrote: > >> I haven't seend any problem about using 64 or 128. And it make much > >> less contention on the locks. Just change it. > > > > Isn't there a issue with having a fixed page count given the > > very different default page sizes across architectures ? > > > > x86 is 4kb pages, while ppc64 uses 64kb pages IIUC. > > > > This would mean current value of 64 pages, would correspond > > to 1/4 MB on x86, and 4 MB on ppc64. The new value would > > be 1/2 MB on x86 and 8 MB on ppc64. >=20 > I saw no difference (on x86 between 64 and 128 pages). Bigger pages > means half the contention on the locks and better for compression (see > next series). 1/4 MB -> 1/2 MB is not all that significant a change, but 1/2 MB vs 8 MB is very significant. I wouldn't be surprised if this difference in values results in rather different performance characteristics for multifd migrate between x86 and ppc64. > > Should we instead be measuring this tunable in units that > > are independant of page size ? eg meansure in KB, with a > > requirement that the value is a multiple of the page size. > > Then set the default to 512 KB ? >=20 > See next patch, I just dropped the tunable altogether. Libvirt don't > want to support it (difficult to explain), and in the past you asked me > to choose a sane value and live with it O:-) > It was good for testing, though. Yep, I think its good if QEMU choose a sane value. I'm just wondering whether the value chosen is actually suitable for non-x86 architectures. > Once there, is there a good value for a network packet? I don't have any particular suggestion here. Probably would have to look at real performance measurements of migration vs guest workload to understand if we've got a good size. > I put it in pages because it facilitates the coding, but doing a: > CONSTANT/qemu_target_page_size() is not going to complicate anything > either. Regards, Daniel --=20 |: https://berrange.com -o- https://www.flickr.com/photos/dberran= ge :| |: https://libvirt.org -o- https://fstop138.berrange.c= om :| |: https://entangle-photo.org -o- https://www.instagram.com/dberran= ge :|