From mboxrd@z Thu Jan 1 00:00:00 1970 From: Rik van Riel Subject: Re: [PATCH v15 16/16] unfair qspinlock: a queue based unfair lock Date: Thu, 09 Apr 2015 09:16:24 -0400 Message-ID: <55267BA8.9060009@redhat.com> References: <1428517939-27968-1-git-send-email-Waiman.Long@hp.com> <20150409070146.GL27490@worktop.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Cc: Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , linux-arch@vger.kernel.org, x86@kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, xen-devel@lists.xenproject.org, kvm@vger.kernel.org, Paolo Bonzini , Konrad Rzeszutek Wilk , Boris Ostrovsky , "Paul E. McKenney" , Linus Torvalds , Raghavendra K T , David Vrabel , Oleg Nesterov , Daniel J Blueman , Scott J Norton , Douglas Hatch To: Peter Zijlstra , Waiman Long Return-path: In-Reply-To: <20150409070146.GL27490@worktop.programming.kicks-ass.net> Sender: linux-arch-owner@vger.kernel.org List-Id: kvm.vger.kernel.org On 04/09/2015 03:01 AM, Peter Zijlstra wrote: > On Wed, Apr 08, 2015 at 02:32:19PM -0400, Waiman Long wrote: >> For a virtual guest with the qspinlock patch, a simple unfair byte lock >> will be used if PV spinlock is not configured in or the hypervisor >> isn't either KVM or Xen. The byte lock works fine with small guest >> of just a few vCPUs. On a much larger guest, however, byte lock can >> have serious performance problem. > > Who cares? There are some people out there running guests with dozens of vCPUs. If the code exists to make those setups run better, is there a good reason not to use it? Having said that, only KVM and Xen seem to support very large guests, and PV spinlock is available there. I believe both VMware and Hyperv have a 32 VCPU limit, anyway. -- All rights reversed