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Wed, 3 Apr 2019 17:40:21 +0000 (UTC) Received: from llong.remote.csb (dhcp-17-19.bos.redhat.com [10.18.17.19]) by smtp.corp.redhat.com (Postfix) with ESMTP id 843A66B2C8; Wed, 3 Apr 2019 17:40:19 +0000 (UTC) Subject: Re: [PATCH v2 3/5] locking/qspinlock: Introduce CNA into the slow path of qspinlock To: Peter Zijlstra Cc: Alex Kogan , linux@armlinux.org.uk, mingo@redhat.com, will.deacon@arm.com, arnd@arndb.de, linux-arch@vger.kernel.org, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, bp@alien8.de, hpa@zytor.com, x86@kernel.org, steven.sistare@oracle.com, daniel.m.jordan@oracle.com, dave.dice@oracle.com, rahul.x.yadav@oracle.com References: <20190329152006.110370-1-alex.kogan@oracle.com> <20190329152006.110370-4-alex.kogan@oracle.com> <60a3a2d8-d222-73aa-2df1-64c9d3fa3241@redhat.com> <20190402094320.GM11158@hirez.programming.kicks-ass.net> <9ec3d8dc-d1e0-1b8a-5e00-ba92b9756c58@redhat.com> <20190403171635.GM4038@hirez.programming.kicks-ass.net> From: Waiman Long Openpgp: preference=signencrypt Autocrypt: addr=longman@redhat.com; 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Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.9.1 MIME-Version: 1.0 In-Reply-To: <20190403171635.GM4038@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.25]); Wed, 03 Apr 2019 17:40:22 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 04/03/2019 01:16 PM, Peter Zijlstra wrote: > On Wed, Apr 03, 2019 at 12:33:20PM -0400, Waiman Long wrote: >> static inline void queued_spin_lock_slowpath(struct qspinlock *lock, u32 >> val) >> { >>         if (static_branch_unlikely(&use_numa_spinlock)) >>                 numa_queued_spin_lock_slowpath(lock, val); >>         else    >>                 native_queued_spin_lock_slowpath(lock, val); >> } > That's horrible for the exact reason you state. > >> Alternatively, we can also call numa_queued_spin_lock_slowpath() in >> native_queued_spin_lock_slowpath() if we don't want to increase the code >> size of spinlock call sites. > Yeah, still don't much like that though, we're littering the fast path > of that slow path with all sorts of crap. Yes, I know it is less than ideal, but that is probably the only option if we don't have static_call or paravirt. On the other hand, I am perfectly fine with making CNA depends on PARAVIRT_SPINLOCKS for now until static_call is available. Cheers, Longman