From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([209.51.188.92]:33957) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1griW6-00045d-RT for qemu-devel@nongnu.org; Thu, 07 Feb 2019 07:10:57 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1griW5-0004cx-VK for qemu-devel@nongnu.org; Thu, 07 Feb 2019 07:10:54 -0500 Received: from mx1.redhat.com ([209.132.183.28]:39954) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1griW5-0004cN-Kb for qemu-devel@nongnu.org; Thu, 07 Feb 2019 07:10:53 -0500 Received: from smtp.corp.redhat.com (int-mx07.intmail.prod.int.phx2.redhat.com [10.5.11.22]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id C91368764B for ; Thu, 7 Feb 2019 12:10:52 +0000 (UTC) From: Juan Quintela In-Reply-To: <20190207113312.GD19438@redhat.com> ("Daniel P. =?utf-8?Q?Ber?= =?utf-8?Q?rang=C3=A9=22's?= message of "Thu, 7 Feb 2019 11:33:12 +0000") References: <20190206132331.1694-1-quintela@redhat.com> <20190206132331.1694-2-quintela@redhat.com> <20190207113312.GD19438@redhat.com> Reply-To: quintela@redhat.com Date: Thu, 07 Feb 2019 13:13:36 +0100 Message-ID: <878syrg5jj.fsf@trasno.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 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: "Daniel P. =?utf-8?Q?Berrang=C3=A9?=" Cc: qemu-devel@nongnu.org, Laurent Vivier , Thomas Huth , Markus Armbruster , "Dr. David Alan Gilbert" , Paolo Bonzini 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. 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). > 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 ? 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. Once there, is there a good value for a network packet? 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. Later, Juan.