Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754472AbaBKUhK (ORCPT ); Tue, 11 Feb 2014 15:37:10 -0500 Received: from gate.crashing.org ([63.228.1.57]:57218 "EHLO gate.crashing.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754364AbaBKUhH (ORCPT ); Tue, 11 Feb 2014 15:37:07 -0500 Message-ID: <1392147268.3835.11.camel@pasglop> Subject: Re: [PATCH v2] powerpc ticket locks From: Benjamin Herrenschmidt To: Scott Wood Cc: Torsten Duwe , Raghavendra KT , Paul Mackerras , Anton Blanchard , "Paul E. McKenney" , Peter Zijlstra , Tom Musta , Ingo Molnar , Linux Kernel Mailing List , linuxppc-dev@lists.ozlabs.org, Raghavendra KT Date: Wed, 12 Feb 2014 06:34:28 +1100 In-Reply-To: <1392143455.6733.386.camel@snotra.buserror.net> References: <20140207165801.GC2107@lst.de> <1392001823.3996.21.camel@pasglop> <20140211104030.GG2107@lst.de> <1392143455.6733.386.camel@snotra.buserror.net> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.8.4-0ubuntu1 Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 2014-02-11 at 12:30 -0600, Scott Wood wrote: > > It's something very special to IBM pSeries: the hypervisor can assign > > fractions of physical CPUs to guests. Sometimes a guest with 4 quarter > > CPUs will be faster than 1 monoprocessor. (correct me if I'm wrong). > > > > The directed yield resolves the silly situation when holder and waiter > > reside on the same physical CPU, as I understand it. > > > > x86 has nothing comparable. > > How is this different from the very ordinary case of an SMP KVM guest > whose vcpus are not bound to host cpus, and thus you could have multiple > vcpus running on the same host cpu? It's not really ... though I can see drawbacks with the scheme as well and I think in KVM we should be careful to only confer if the owner vcpu last scheduled on the same physical cpu where the waiter is, other wise, there's too much chances of us bouncing things around the machine for minor contention cases. Paul, what's your policy today ? Cheers, Ben. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/