From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:40449) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1W1cow-00085z-Do for qemu-devel@nongnu.org; Fri, 10 Jan 2014 09:12:29 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1W1col-0001kX-TW for qemu-devel@nongnu.org; Fri, 10 Jan 2014 09:12:22 -0500 Received: from mail-qe0-f51.google.com ([209.85.128.51]:54454) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1W1col-0001kK-Ps for qemu-devel@nongnu.org; Fri, 10 Jan 2014 09:12:11 -0500 Received: by mail-qe0-f51.google.com with SMTP id 1so4615302qee.10 for ; Fri, 10 Jan 2014 06:12:11 -0800 (PST) From: Mike Day In-Reply-To: <84B5F34E-6072-4E56-8493-AAC69B9F7DAE@suse.de> References: <1389245648-10300-1-git-send-email-aik@ozlabs.ru> <87ppo0na45.fsf@pixel.localdomain> <52CF1ECC.3040208@ozlabs.ru> <52CF4F37.4050306@ozlabs.ru> <878uuof0pu.fsf@pixel.localdomain> <84B5F34E-6072-4E56-8493-AAC69B9F7DAE@suse.de> Date: Fri, 10 Jan 2014 09:12:09 -0500 Message-ID: <8761psexja.fsf@pixel.localdomain> MIME-Version: 1.0 Content-Type: text/plain Subject: Re: [Qemu-devel] [RFC PATCH v2] PPC: smp: autodetect numbers of threads per core List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alexander Graf Cc: Alexey Kardashevskiy , Paul Mackerras , "qemu-ppc@nongnu.org" , "qemu-devel@nongnu.org" Alexander Graf writes: >> The patch as it its now is very simple and well-contained. I wonder how >> much it would expand if we added a max thread count to the cpu class. It >> seems like the need for a max thread count is idiomatic to powerpc. > > It's only ever useful on IBM POWER. Any other PowerPC system can partition vcpus by host threads, it's only IBM POWER hardware that's as broken as it is. > I do see that the user experience is slightly suboptimal, but by creating this special case there's a good chance you're doing more harm than good. All the problems you raise about special cases are true. But, as you point out, ibm power is uniquely broken, which would possibly justify a special case, unless there is a better general solution. In other words, special cases exist for unique circumstances and if I understand you correctly this is a unique circumstance. Alexy explained the use case in his initial posting. The user needs to allocate all threads of a core to an instance of KVM, but has no easy way to obtain that information (threads per core) for the Qemu threads option. So specifying threads="max" is a more user-friendly option. In my understanding this is strictly a usability issue. Mike -- Mike Day | "Endurance is a Virtue"