From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH v2 3/5] locking/qspinlock: Introduce CNA into the slow path of qspinlock Date: Wed, 3 Apr 2019 19:16:35 +0200 Message-ID: <20190403171635.GM4038@hirez.programming.kicks-ass.net> 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> Mime-Version: 1.0 Content-Type: text/plain; charset="iso-8859-1" Content-Transfer-Encoding: quoted-printable Return-path: Content-Disposition: inline In-Reply-To: <9ec3d8dc-d1e0-1b8a-5e00-ba92b9756c58@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=m.gmane.org@lists.infradead.org To: Waiman Long Cc: linux-arch@vger.kernel.org, arnd@arndb.de, dave.dice@oracle.com, x86@kernel.org, will.deacon@arm.com, linux@armlinux.org.uk, linux-kernel@vger.kernel.org, rahul.x.yadav@oracle.com, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, Alex Kogan , steven.sistare@oracle.com, tglx@linutronix.de, daniel.m.jordan@oracle.com, linux-arm-kernel@lists.infradead.org List-Id: linux-arch.vger.kernel.org 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) > { > =A0=A0=A0=A0=A0=A0=A0 if (static_branch_unlikely(&use_numa_spinlock)) > =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 numa_queued_spin_lock_slowp= ath(lock, val); > =A0=A0=A0=A0=A0=A0=A0 else=A0=A0=A0 > =A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0=A0 native_queued_spin_lock_slo= wpath(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. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from bombadil.infradead.org ([198.137.202.133]:41786 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726074AbfDCRQt (ORCPT ); Wed, 3 Apr 2019 13:16:49 -0400 Date: Wed, 3 Apr 2019 19:16:35 +0200 From: Peter Zijlstra Subject: Re: [PATCH v2 3/5] locking/qspinlock: Introduce CNA into the slow path of qspinlock Message-ID: <20190403171635.GM4038@hirez.programming.kicks-ass.net> 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> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <9ec3d8dc-d1e0-1b8a-5e00-ba92b9756c58@redhat.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Waiman Long 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 Message-ID: <20190403171635.wkDc8881XOlxxAeF67Ow576HiK8H4NuOqouAZYgrXBA@z> 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.