From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:44967) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1a1EXU-0006Em-Ru for qemu-devel@nongnu.org; Tue, 24 Nov 2015 09:25:50 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1a1EXQ-00038f-Vu for qemu-devel@nongnu.org; Tue, 24 Nov 2015 09:25:48 -0500 Received: from mx1.redhat.com ([209.132.183.28]:33040) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1a1EXQ-00038I-Ja for qemu-devel@nongnu.org; Tue, 24 Nov 2015 09:25:44 -0500 Date: Tue, 24 Nov 2015 16:25:40 +0200 From: "Michael S. Tsirkin" Message-ID: <20151124162004-mutt-send-email-mst@redhat.com> References: <1447694618-17177-3-git-send-email-marcandre.lureau@redhat.com> <1447837378-25222-1-git-send-email-marcandre.lureau@redhat.com> <20151118224821-mutt-send-email-mst@redhat.com> <56534FAA.4090101@redhat.com> <20151123181008.GU18085@redhat.com> <20151124160921-mutt-send-email-mst@redhat.com> <20151124141936.GJ9981@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline In-Reply-To: <20151124141936.GJ9981@redhat.com> Content-Transfer-Encoding: quoted-printable Subject: Re: [Qemu-devel] [PATCH] exec: silence hugetlbfs warning under qtest List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Daniel P. Berrange" Cc: Amit Shah , Paolo Bonzini , =?iso-8859-1?Q?Marc-Andr=E9?= Lureau , QEMU , Peter Maydell On Tue, Nov 24, 2015 at 02:19:36PM +0000, Daniel P. Berrange wrote: > On Tue, Nov 24, 2015 at 04:10:54PM +0200, Michael S. Tsirkin wrote: > > On Mon, Nov 23, 2015 at 06:10:08PM +0000, Daniel P. Berrange wrote: > > > On Mon, Nov 23, 2015 at 07:01:33PM +0100, Marc-Andr=E9 Lureau wrote= : > > > > On Mon, Nov 23, 2015 at 6:40 PM, Paolo Bonzini wrote: > > > > > Before: object-initial, chardev, qtest, object-late (not in the= patch) > > > > > > > > > > After: chardev, qtest, object-initial, object-late (not in the = patch) > > > > > > > > > > Objects must be initialized before chardev (except rng-egd) sin= ce in the > > > > > future chardev will need to use objects, in particular secret o= bjects. > > > > > Was the swap intentional? > > > >=20 > > > > Yes, without the swap, qtest was not initialized before memory is= allocated. > > > >=20 > > > > The alternative I could think of is to check the QTEST_QEMU_BINAR= Y > > > > variable: http://lists.nongnu.org/archive/html/qemu-devel/2015-11= /msg01527.html > > >=20 > > > Why do we not simply delete the warning message about the path not > > > being on hugetlbfs ? ie, why does QEMU try to force a policy that > > > a memory-file backend has to be on hugetlbfs, as opposed to on > > > a plain tmpfs ? I've previously had user request that we allow > > > use of plain tmpfs, because they want to use vhost-user without > > > also using hugepages, and that could be done with plain tmpfs. > >=20 > > Because THP does not work on any other filesystem, > > so many workloads are much slower. > > That's why it's a warning, not an error. >=20 > AFAICT this warning message is not in a codepath that is specific to > use of THP. This is just generic code for allocating guest memory > backed by a file, which does not have any assumption / prerequisite > that THP is wanted or enabled. So adding warnings that are specifically > related to THP is inappropriate. >=20 > The fact that THP only works with a hugetlbfs path is merely a > documentation item to record against the command line option for > -mem-path. I'm worried that things go slow and people don't have a way to find out why, and documentation isn't the first place people look for when facing a performance issue. At the moment we call MADV_HUGEPAGE unconditionally and unfortunately there's no way to report it's not having the intended effect. Maybe we want a "don't enable hugepages" flag. That could also have the effect of suppressing the warnings. >=20 > Regards, > Daniel > --=20 > |: http://berrange.com -o- http://www.flickr.com/photos/dberran= ge/ :| > |: http://libvirt.org -o- http://virt-manager.= org :| > |: http://autobuild.org -o- http://search.cpan.org/~danbe= rr/ :| > |: http://entangle-photo.org -o- http://live.gnome.org/gtk-= vnc :|