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: Mon, 1 Apr 2019 11:33:45 +0200 Message-ID: <20190401093345.GA14281@hirez.programming.kicks-ass.net> References: <20190329152006.110370-1-alex.kogan@oracle.com> <20190329152006.110370-4-alex.kogan@oracle.com> <20190401090653.GF11158@hirez.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <20190401090653.GF11158@hirez.programming.kicks-ass.net> 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: Alex Kogan Cc: linux-arch@vger.kernel.org, arnd@arndb.de, dave.dice@oracle.com, x86@kernel.org, will.deacon@arm.com, linux@armlinux.org.uk, steven.sistare@oracle.com, linux-kernel@vger.kernel.org, rahul.x.yadav@oracle.com, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, longman@redhat.com, tglx@linutronix.de, daniel.m.jordan@oracle.com, linux-arm-kernel@lists.infradead.org List-Id: linux-arch.vger.kernel.org On Mon, Apr 01, 2019 at 11:06:53AM +0200, Peter Zijlstra wrote: > On Fri, Mar 29, 2019 at 11:20:04AM -0400, Alex Kogan wrote: > > diff --git a/kernel/locking/mcs_spinlock.h b/kernel/locking/mcs_spinlock.h > > index bc6d3244e1af..71ee4b64c5d4 100644 > > --- a/kernel/locking/mcs_spinlock.h > > +++ b/kernel/locking/mcs_spinlock.h > > @@ -17,8 +17,18 @@ > > > > struct mcs_spinlock { > > struct mcs_spinlock *next; > > +#ifndef CONFIG_NUMA_AWARE_SPINLOCKS > > int locked; /* 1 if lock acquired */ > > int count; /* nesting count, see qspinlock.c */ > > +#else /* CONFIG_NUMA_AWARE_SPINLOCKS */ > > + uintptr_t locked; /* 1 if lock acquired, 0 if not, other values */ > > + /* represent a pointer to the secondary queue head */ > > + u32 node_and_count; /* node id on which this thread is running */ > > + /* with two lower bits reserved for nesting */ > > + /* count, see qspinlock.c */ > > + u32 encoded_tail; /* encoding of this node as the main queue tail */ > > + struct mcs_spinlock *tail; /* points to the secondary queue tail */ > > +#endif /* CONFIG_NUMA_AWARE_SPINLOCKS */ > > }; > > Please, have another look at the paravirt code, in particular at struct > pv_node and its usage. This is horrible. Thing is, this turns into a right mess when you also have PV spinlocks on. One thing we could maybe do is change locked and count to u8, then your overlay structure could be something like: struct mcs_spinlock { struct mcs_spinlock *next; u8 locked; u8 count; }; struct cna_node { /* struct mcs_spinlock overlay */ struct mcs_spinlock *next; u8 locked; u8 count; /* our CNA bits, consuming the slack and PV space */ u16 node; u32 encoded_tail; struct mcs_spinlock *head; struct mcs_spinlock *tail; }; Then you also don't need the first two patches. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from merlin.infradead.org ([205.233.59.134]:36952 "EHLO merlin.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725832AbfDAJeJ (ORCPT ); Mon, 1 Apr 2019 05:34:09 -0400 Date: Mon, 1 Apr 2019 11:33:45 +0200 From: Peter Zijlstra Subject: Re: [PATCH v2 3/5] locking/qspinlock: Introduce CNA into the slow path of qspinlock Message-ID: <20190401093345.GA14281@hirez.programming.kicks-ass.net> References: <20190329152006.110370-1-alex.kogan@oracle.com> <20190329152006.110370-4-alex.kogan@oracle.com> <20190401090653.GF11158@hirez.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190401090653.GF11158@hirez.programming.kicks-ass.net> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Alex Kogan Cc: linux@armlinux.org.uk, mingo@redhat.com, will.deacon@arm.com, arnd@arndb.de, longman@redhat.com, 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: <20190401093345.k8CvgOpMofAXUHi3tC0MMpok9o9_Rin6SVEhOWDE5Ok@z> On Mon, Apr 01, 2019 at 11:06:53AM +0200, Peter Zijlstra wrote: > On Fri, Mar 29, 2019 at 11:20:04AM -0400, Alex Kogan wrote: > > diff --git a/kernel/locking/mcs_spinlock.h b/kernel/locking/mcs_spinlock.h > > index bc6d3244e1af..71ee4b64c5d4 100644 > > --- a/kernel/locking/mcs_spinlock.h > > +++ b/kernel/locking/mcs_spinlock.h > > @@ -17,8 +17,18 @@ > > > > struct mcs_spinlock { > > struct mcs_spinlock *next; > > +#ifndef CONFIG_NUMA_AWARE_SPINLOCKS > > int locked; /* 1 if lock acquired */ > > int count; /* nesting count, see qspinlock.c */ > > +#else /* CONFIG_NUMA_AWARE_SPINLOCKS */ > > + uintptr_t locked; /* 1 if lock acquired, 0 if not, other values */ > > + /* represent a pointer to the secondary queue head */ > > + u32 node_and_count; /* node id on which this thread is running */ > > + /* with two lower bits reserved for nesting */ > > + /* count, see qspinlock.c */ > > + u32 encoded_tail; /* encoding of this node as the main queue tail */ > > + struct mcs_spinlock *tail; /* points to the secondary queue tail */ > > +#endif /* CONFIG_NUMA_AWARE_SPINLOCKS */ > > }; > > Please, have another look at the paravirt code, in particular at struct > pv_node and its usage. This is horrible. Thing is, this turns into a right mess when you also have PV spinlocks on. One thing we could maybe do is change locked and count to u8, then your overlay structure could be something like: struct mcs_spinlock { struct mcs_spinlock *next; u8 locked; u8 count; }; struct cna_node { /* struct mcs_spinlock overlay */ struct mcs_spinlock *next; u8 locked; u8 count; /* our CNA bits, consuming the slack and PV space */ u16 node; u32 encoded_tail; struct mcs_spinlock *head; struct mcs_spinlock *tail; }; Then you also don't need the first two patches.