From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e1.ny.us.ibm.com (e1.ny.us.ibm.com [32.97.182.141]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "e1.ny.us.ibm.com", Issuer "Equifax" (verified OK)) by ozlabs.org (Postfix) with ESMTPS id D786FDE9E2 for ; Thu, 21 Aug 2008 05:07:01 +1000 (EST) Received: from d01relay07.pok.ibm.com (d01relay07.pok.ibm.com [9.56.227.147]) by e1.ny.us.ibm.com (8.13.8/8.13.8) with ESMTP id m7KJ6snL016555 for ; Wed, 20 Aug 2008 15:06:54 -0400 Received: from d03av02.boulder.ibm.com (d03av02.boulder.ibm.com [9.17.195.168]) by d01relay07.pok.ibm.com (8.13.8/8.13.8/NCO v9.0) with ESMTP id m7KJ6rqs1839114 for ; Wed, 20 Aug 2008 15:06:53 -0400 Received: from d03av02.boulder.ibm.com (loopback [127.0.0.1]) by d03av02.boulder.ibm.com (8.12.11.20060308/8.13.3) with ESMTP id m7KJ6qJB017504 for ; Wed, 20 Aug 2008 13:06:52 -0600 Subject: Re: [PATCH 4/4] kvmppc: convert wrteei to wrtee as kvm guest optimization From: Hollis Blanchard To: jwboyer@linux.vnet.ibm.com In-Reply-To: <1219258333.26429.29.camel@jdub.homelinux.org> References: <1219142204-12044-1-git-send-email-ehrhardt@linux.vnet.ibm.com> <1219142204-12044-5-git-send-email-ehrhardt@linux.vnet.ibm.com> <200808191342.29918.arnd@arndb.de> <48AC13E5.5010503@linux.vnet.ibm.com> <1219257000.14362.90.camel@localhost.localdomain> <1219258333.26429.29.camel@jdub.homelinux.org> Content-Type: text/plain Date: Wed, 20 Aug 2008 14:06:51 -0500 Message-Id: <1219259211.14362.94.camel@localhost.localdomain> Mime-Version: 1.0 Cc: Arnd Bergmann , kvm-ppc@vger.kernel.org, linuxppc-dev@ozlabs.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Wed, 2008-08-20 at 14:52 -0400, Josh Boyer wrote: > On Wed, 2008-08-20 at 13:30 -0500, Hollis Blanchard wrote: > > On Wed, 2008-08-20 at 14:53 +0200, Christian Ehrhardt wrote: > > > > > > Arnd Bergmann wrote: > > > > On Tuesday 19 August 2008, ehrhardt@linux.vnet.ibm.com wrote: > > > > > > > >> Dependent on the already existing CONFIG_KVM_GUEST config option > > > this patch > > > >> changes wrteei to wrtee allowing the hypervisor to rewrite those to > > > nontrapping > > > >> instructions. Maybe we should split the kvm guest otpimizations in > > > two parts > > > >> one for the overhead free optimizations and on for the rest that > > > might add > > > >> some complexity for non virtualized execution (like this one). > > > >> > > > >> Signed-off-by: Christian Ehrhardt > > > >> > > > > > > > > How significant is the performance impact of this change for > > > non-virtualized > > > > systems? If it's very low, maybe you should not bother with the > > > #ifdef, and > > > > if it's noticable, you might be better off using dynamic patching > > > for this. > > > > > > > > Arnd <>< > > > > > > > To be honest I unfortunately don't know how big the impact for > > > non-virtualized systems is. I would like to test it, but without > > > hardware performance counters on the core I have I'm not sure (yet) > > > how > > > to measure that in a good way - any suggestion welcome. > > > > I don't see why we need performance counters. Can't we just compare any > > bare metal benchmark results with the patch both applied and not? > > Do you know of one that causes a large amount of > local_irq_{disable,enable}s to be called? I think *every* workload causes a large number of local_irq_{disable,enable} calls... :) -- Hollis Blanchard IBM Linux Technology Center