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Wed, 08 Jul 2020 19:53:08 -0400 X-MC-Unique: PttZH5YuNPOhfnms_liwDg-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 30B6F1082; Wed, 8 Jul 2020 23:53:06 +0000 (UTC) Received: from llong.remote.csb (ovpn-116-205.rdu2.redhat.com [10.10.116.205]) by smtp.corp.redhat.com (Postfix) with ESMTP id EA6637F8A4; Wed, 8 Jul 2020 23:53:04 +0000 (UTC) Subject: Re: [PATCH v3 0/6] powerpc: queued spinlocks and rwlocks To: Peter Zijlstra 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> From: Waiman Long Organization: Red Hat Message-ID: <72f7df33-ab58-2e58-7981-cf02b6638c5b@redhat.com> Date: Wed, 8 Jul 2020 19:53:04 -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: <20200708083210.GD597537@hirez.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 2.79 on 10.5.11.15 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, Will Deacon , Boqun Feng , linux-kernel@vger.kernel.org, kvm-ppc@vger.kernel.org, virtualization@lists.linux-foundation.org, Ingo Molnar , Nicholas Piggin , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" 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