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Thu, 23 Jul 2020 18:32:38 +0000 (UTC) Received: from llong.remote.csb (ovpn-119-128.rdu2.redhat.com [10.10.119.128]) by smtp.corp.redhat.com (Postfix) with ESMTP id 209FA19D7E; Thu, 23 Jul 2020 18:32:37 +0000 (UTC) Subject: Re: [PATCH v3 5/6] powerpc/pseries: implement paravirt qspinlocks for SPLPAR To: Peter Zijlstra 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> From: Waiman Long Organization: Red Hat Message-ID: <845de183-56f5-2958-3159-faa131d46401@redhat.com> Date: Thu, 23 Jul 2020 14:32:36 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.4.1 MIME-Version: 1.0 In-Reply-To: <20200723140011.GR5523@worktop.programming.kicks-ass.net> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch@vger.kernel.org, Boqun Feng , virtualization@lists.linux-foundation.org, linuxppc-dev@lists.ozlabs.org, Nicholas Piggin , linux-kernel@vger.kernel.org, Ingo Molnar , kvm-ppc@vger.kernel.org, Will Deacon Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" 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