From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andi Kleen Subject: Re: [PATCH 1/3] Introduce cpuid_on_cpu() and cpuid_eax_on_cpu() Date: Tue, 3 Apr 2007 15:42:50 +0200 Message-ID: <200704031542.50630.ak@suse.de> References: <20070402113831.GA6785@localhost.sw.ru> <200704021410.29623.ak@suse.de> <20070403133946.GA6536@localhost.sw.ru> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20070403133946.GA6536@localhost.sw.ru> Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-Id: Content-Type: text/plain; charset="us-ascii" To: Alexey Dobriyan Cc: akpm@osdl.org, linux-kernel@vger.kernel.org, devel@openvz.org, cpufreq@lists.linux.org.uk, hpa@zytor.com, davej@codemonkey.org.uk > > Both powernow-k8 and cpuid attempt to schedule > > to the target CPU so they should already run there. But it is some other CPU, > > but when they ask your _on_cpu() functions they suddenly get a "real" CPU? > > Where is the difference between these levels of virtualness? > > *_on_cpu functions do some work on given physical CPU. > set_cpus_allowed() in openvz operates on VCPU level, so process doing > set_cpus_allowed() still could be scheduled anywhere. Ok so you have multple levels. > > Also it has weird semantics. For example if you have multiple > > virtual CPUs mapping to a single CPU then would the powernow-k8 driver > > try to set the frequency multiple times on the same physical CPU? > > If core cpufreq locking is OK, why would it? It won't know about multiple CPUs mapping to a single CPU. > apply_microcode() looks small enough to convert it to IPIs, but so far > nobody asked for microcode updates in openvz. Well if they try it they will probably have problems. > > Before adding any hacks like this I think your vcpu concept > > needs to be discussed properly on l-k. For me it doesn't look like it is > > something good right now though. > > Andi, I think it all relies on correctness of core cpufreq locking. I have my doubts it will cope with you changing all reasonable expected semantics under it. -Andi