From mboxrd@z Thu Jan 1 00:00:00 1970 From: Waiman Long Subject: Re: [PATCH v3 5/6] powerpc/pseries: implement paravirt qspinlocks for SPLPAR Date: Thu, 23 Jul 2020 14:32:36 -0400 Message-ID: <845de183-56f5-2958-3159-faa131d46401@redhat.com> References: <20200706043540.1563616-1-npiggin@gmail.com> <20200706043540.1563616-6-npiggin@gmail.com> <874kqhvu1v.fsf@mpe.ellerman.id.au> <8265d782-4e50-a9b2-a908-0cb588ffa09c@redhat.com> <20200723140011.GR5523@worktop.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20200723140011.GR5523@worktop.programming.kicks-ass.net> Content-Language: en-US Sender: linux-arch-owner@vger.kernel.org To: Peter Zijlstra Cc: Michael Ellerman , Nicholas Piggin , linuxppc-dev@lists.ozlabs.org, Will Deacon , Boqun Feng , Ingo Molnar , Anton Blanchard , linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, kvm-ppc@vger.kernel.org, linux-arch@vger.kernel.org List-Id: virtualization@lists.linuxfoundation.org On 7/23/20 10:00 AM, Peter Zijlstra wrote: > On Thu, Jul 09, 2020 at 12:06:13PM -0400, Waiman Long wrote: >> We don't really need to do a pv_spinlocks_init() if pv_kick() isn't >> supported. > Waiman, if you cannot explain how not having kick is a sane thing, what > are you saying here? > The current PPC paravirt spinlock code doesn't do any cpu kick. It does an equivalence of pv_wait by yielding the cpu to the lock holder only. The pv_spinlocks_init() is for setting up the hash table for doing pv_kick. If we don't need to do pv_kick, we don't need the hash table. I am not saying that pv_kick is not needed for the PPC environment. I was just trying to adapt the pvqspinlock code to such an environment first. Further investigation on how to implement some kind of pv_kick will be something that we may want to do as a follow on. BTW, do you have any comment on my v2 lock holder cpu info qspinlock patch? I will have to update the patch to fix the reported 0-day test problem, but I want to collect other feedback before sending out v3. Cheers, Longman