From mboxrd@z Thu Jan 1 00:00:00 1970 From: Waiman Long Subject: Re: [PATCH v3 0/6] powerpc: queued spinlocks and rwlocks Date: Wed, 8 Jul 2020 19:53:04 -0400 Message-ID: <72f7df33-ab58-2e58-7981-cf02b6638c5b@redhat.com> References: <20200706043540.1563616-1-npiggin@gmail.com> <24f75d2c-60cd-2766-4aab-1a3b1c80646e@redhat.com> <1594101082.hfq9x5yact.astroid@bobo.none> <20200708083210.GD597537@hirez.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: <20200708083210.GD597537@hirez.programming.kicks-ass.net> Content-Language: en-US Sender: kvm-ppc-owner@vger.kernel.org To: Peter Zijlstra Cc: Nicholas Piggin , linuxppc-dev@lists.ozlabs.org, Anton Blanchard , Boqun Feng , kvm-ppc@vger.kernel.org, linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, Ingo Molnar , virtualization@lists.linux-foundation.org, Will Deacon List-Id: virtualization@lists.linuxfoundation.org On 7/8/20 4:32 AM, Peter Zijlstra wrote: > On Tue, Jul 07, 2020 at 11:33:45PM -0400, Waiman Long wrote: >> From 5d7941a498935fb225b2c7a3108cbf590114c3db Mon Sep 17 00:00:00 2001 >> From: Waiman Long >> Date: Tue, 7 Jul 2020 22:29:16 -0400 >> Subject: [PATCH 2/9] locking/pvqspinlock: Introduce >> CONFIG_PARAVIRT_QSPINLOCKS_LITE >> >> Add a new PARAVIRT_QSPINLOCKS_LITE config option that allows >> architectures to use the PV qspinlock code without the need to use or >> implement a pv_kick() function, thus eliminating the atomic unlock >> overhead. The non-atomic queued_spin_unlock() can be used instead. >> The pv_wait() function will still be needed, but it can be a dummy >> function. >> >> With that option set, the hybrid PV queued/unfair locking code should >> still be able to make it performant enough in a paravirtualized > How is this supposed to work? If there is no kick, you have no control > over who wakes up and fairness goes out the window entirely. > > You don't even begin to explain... > I don't have a full understanding of how the PPC hypervisor work myself. Apparently, a cpu kick may not be needed. This is just a test patch to see if it yields better result. It is subjected to further modifcation. Cheers, Longman