From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:43232) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1brPod-00008J-MH for qemu-devel@nongnu.org; Tue, 04 Oct 2016 09:31:33 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1brPoX-00006A-IV for qemu-devel@nongnu.org; Tue, 04 Oct 2016 09:31:26 -0400 Received: from mx1.redhat.com ([209.132.183.28]:44150) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1brPoX-00005R-Bx for qemu-devel@nongnu.org; Tue, 04 Oct 2016 09:31:21 -0400 Date: Tue, 4 Oct 2016 14:31:14 +0100 From: "Daniel P. Berrange" Message-ID: <20161004133114.GL5578@redhat.com> Reply-To: "Daniel P. Berrange" References: <1475580648-6470-1-git-send-email-lvivier@redhat.com> <1475580648-6470-2-git-send-email-lvivier@redhat.com> <4a11fc7e-ccec-2252-c356-a0ca3466bbf0@redhat.com> <912a8fc8-47bd-fffe-60ff-0cd7b006402c@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <912a8fc8-47bd-fffe-60ff-0cd7b006402c@redhat.com> Subject: Re: [Qemu-devel] [PATCH 1/2] accel: allows to select the "best" accelerator List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Thomas Huth Cc: Paolo Bonzini , Laurent Vivier , Peter Maydell , "Michael S . Tsirkin" , Alex =?utf-8?Q?Benn=C3=A9e?= , qemu-devel@nongnu.org, Stefano Stabellini On Tue, Oct 04, 2016 at 02:49:21PM +0200, Thomas Huth wrote: > On 04.10.2016 14:41, Paolo Bonzini wrote: > > > > > > On 04/10/2016 13:30, Laurent Vivier wrote: > >> But sometime, user wants to use a real accelerator without knowing > >> if he really can, with, for instance accel=kvm:tcg. > >> In this case, and if the accelerator is not available we > >> have a noisy "XXX accelerator not found". > >> > >> By allowing the user to ask the "best" accelerator for the given > >> target, we can avoid this problem. > >> > >> This patch introduces a new parameter for the "accel" property, the > >> "best" keyword. > >> > >> You can ask to use the best accelerator with "-M accel=best", > >> or if you want to use your favorite accelerator and if it is not > >> available, the best one, you can use, for instance > >> "-M accel=kvm:best". > > > > I don't think there's a single definition of a "best" accelerator. For > > example, some "-cpu" features may be available only with TCG. In that > > case, "kvm:tcg" has a clear meaning ("kvm" if it exists, otherwise > > "tcg") but "best" doesn't. > > > > I agree with Daniel that unit tests should use "tcg" exclusively, at > > least as a default. > > Using only tcg has also some disadvantages: For some tests, it's > interesting to know whether they also work properly with KVM (e.g. > migration tests), and only using tcg by default slows down the "make > check" quite a bit - which might become an issue now that we're adding > more and more tests. Which tests are you seeing a slow-down for ? make check-unit doesn't show any difference and for 'make check-qtest' the difference was negligible (1m47 for KVM vs 1m57 for TCG). We shouldn't be running extensive guest workloads in unit tests, so I'd be surprised to see a major hit in unit test time. Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://entangle-photo.org -o- http://search.cpan.org/~danberr/ :|