From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:38662) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1eJtoj-0006Wr-9t for qemu-devel@nongnu.org; Tue, 28 Nov 2017 23:17:50 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1eJtoe-000399-9x for qemu-devel@nongnu.org; Tue, 28 Nov 2017 23:17:49 -0500 Received: from mx1.redhat.com ([209.132.183.28]:51804) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1eJtoe-00038l-3B for qemu-devel@nongnu.org; Tue, 28 Nov 2017 23:17:44 -0500 Date: Wed, 29 Nov 2017 06:17:40 +0200 From: "Michael S. Tsirkin" Message-ID: <20171129061258-mutt-send-email-mst@kernel.org> References: <1511530010-511740-1-git-send-email-dplotnikov@virtuozzo.com> <20171128195817.GA29077@localhost.localdomain> <2cd31202-27c3-983f-85a9-6814ff504706@virtuozzo.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2cd31202-27c3-983f-85a9-6814ff504706@virtuozzo.com> Subject: Re: [Qemu-devel] [PATCH] i386: turn off l3-cache property by default List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Denis V. Lunev" Cc: Eduardo Habkost , Denis Plotnikov , pbonzini@redhat.com, rth@twiddle.net, qemu-devel@nongnu.org, rkagan@virtuozzo.com On Tue, Nov 28, 2017 at 11:20:27PM +0300, Denis V. Lunev wrote: > > There's one thing I don't understand in your test case: if you > > just found out that Linux will behave worse if it assumes that > > the VCPUs are sharing a L3 cache, why are you configuring a > > 8-core VCPU topology explicitly? > > > > Do you still see a difference in the numbers if you use "-smp 8" > > with no "cores" and "threads" options? > > > This is quite simple. A lot of software licenses are bound to the amount > of CPU __sockets__. Thus it is mandatory in a lot of cases to set topology > with 1 socket/xx cores to reduce the amount of money necessary to > be paid for the software. This answers the first question but not the second one. If the answer to the second one is negative, then I don't understand why changing the default makes sense. I would expect qemu by default to be as close to emulating a physical system as possible. If one has to deviate from that for some workloads, that is fine, but probably not a good default. -- MST