From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 09AF0C7618F for ; Mon, 15 Jul 2019 21:30:08 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BB4CF2145D for ; Mon, 15 Jul 2019 21:30:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1731763AbfGOVaG (ORCPT ); Mon, 15 Jul 2019 17:30:06 -0400 Received: from mx1.redhat.com ([209.132.183.28]:40596 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730156AbfGOVaG (ORCPT ); Mon, 15 Jul 2019 17:30:06 -0400 Received: from smtp.corp.redhat.com (int-mx08.intmail.prod.int.phx2.redhat.com [10.5.11.23]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 4F60E4E93D; Mon, 15 Jul 2019 21:30:05 +0000 (UTC) Received: from llong.remote.csb (dhcp-17-160.bos.redhat.com [10.18.17.160]) by smtp.corp.redhat.com (Postfix) with ESMTP id 4242319C59; Mon, 15 Jul 2019 21:30:02 +0000 (UTC) Subject: Re: [PATCH v3 3/5] locking/qspinlock: Introduce CNA into the slow path of qspinlock To: Alex Kogan , linux@armlinux.org.uk, peterz@infradead.org, 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, guohanjun@huawei.com, jglauber@marvell.com Cc: steven.sistare@oracle.com, daniel.m.jordan@oracle.com, dave.dice@oracle.com, rahul.x.yadav@oracle.com References: <20190715192536.104548-1-alex.kogan@oracle.com> <20190715192536.104548-4-alex.kogan@oracle.com> From: Waiman Long Organization: Red Hat Message-ID: <77bba626-f3e6-45a8-aae8-43b945d0fab9@redhat.com> Date: Mon, 15 Jul 2019 17:30:01 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: <20190715192536.104548-4-alex.kogan@oracle.com> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-Scanned-By: MIMEDefang 2.84 on 10.5.11.23 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.38]); Mon, 15 Jul 2019 21:30:05 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/15/19 3:25 PM, Alex Kogan wrote: > In CNA, spinning threads are organized in two queues, a main queue for > threads running on the same node as the current lock holder, and a > secondary queue for threads running on other nodes. At the unlock time, > the lock holder scans the main queue looking for a thread running on > the same node. If found (call it thread T), all threads in the main queue > between the current lock holder and T are moved to the end of the > secondary queue, and the lock is passed to T. If such T is not found, the > lock is passed to the first node in the secondary queue. Finally, if the > secondary queue is empty, the lock is passed to the next thread in the > main queue. For more details, see https://arxiv.org/abs/1810.05600. > > Note that this variant of CNA may introduce starvation by continuously > passing the lock to threads running on the same node. This issue > will be addressed later in the series. > > Enabling CNA is controlled via a new configuration option > (NUMA_AWARE_SPINLOCKS). The CNA variant is patched in > at the boot time only if we run a multi-node machine, and the new > config is enabled. For the time being, the patching requires > CONFIG_PARAVIRT_SPINLOCKS to be enabled as well. > However, this should be resolved once static_call() is available. > > Signed-off-by: Alex Kogan > Reviewed-by: Steve Sistare > --- > arch/x86/Kconfig | 18 +++++ > arch/x86/include/asm/qspinlock.h | 4 + > arch/x86/kernel/alternative.c | 12 +++ > kernel/locking/mcs_spinlock.h | 2 +- > kernel/locking/qspinlock.c | 41 +++++++--- > kernel/locking/qspinlock_cna.h | 164 +++++++++++++++++++++++++++++++++++++++ > 6 files changed, 229 insertions(+), 12 deletions(-) > create mode 100644 kernel/locking/qspinlock_cna.h > > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig > index 2bbbd4d1ba31..1d8f80c47687 100644 > --- a/arch/x86/Kconfig > +++ b/arch/x86/Kconfig > @@ -1548,6 +1548,24 @@ config NUMA > > Otherwise, you should say N. > > +config NUMA_AWARE_SPINLOCKS > + bool "Numa-aware spinlocks" > + depends on NUMA > + # For now, we depend on PARAVIRT_SPINLOCKS to make the patching work. > + # This is awkward, but hopefully would be resolved once static_call() > + # is available. > + depends on PARAVIRT_SPINLOCKS > + default y > + help > + Introduce NUMA (Non Uniform Memory Access) awareness into > + the slow path of spinlocks. > + > + The kernel will try to keep the lock on the same node, > + thus reducing the number of remote cache misses, while > + trading some of the short term fairness for better performance. > + > + Say N if you want absolute first come first serve fairness. You should also add a dependency on QUEUED_SPINLOCKS to highlight the fact that it is a variant of qspinlock. You should also mention that in the help text. > + > config AMD_NUMA > def_bool y > prompt "Old style AMD Opteron NUMA detection" > diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h > index bd5ac6cc37db..d9b6c34d5eb4 100644 > --- a/arch/x86/include/asm/qspinlock.h > +++ b/arch/x86/include/asm/qspinlock.h > @@ -27,6 +27,10 @@ static __always_inline u32 queued_fetch_set_pending_acquire(struct qspinlock *lo > return val; > } > > +#ifdef CONFIG_NUMA_AWARE_SPINLOCKS > +extern void __cna_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val); > +#endif > + > #ifdef CONFIG_PARAVIRT_SPINLOCKS > extern void native_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val); > extern void __pv_init_lock_hash(void); > diff --git a/arch/x86/kernel/alternative.c b/arch/x86/kernel/alternative.c > index 0d57015114e7..1c25f0505ec0 100644 > --- a/arch/x86/kernel/alternative.c > +++ b/arch/x86/kernel/alternative.c > @@ -649,6 +649,18 @@ void __init alternative_instructions(void) > (unsigned long)__smp_locks_end); > #endif > > +#if defined(CONFIG_NUMA_AWARE_SPINLOCKS) > + /* > + * If we have multiple NUMA nodes, switch from native > + * to the NUMA-friendly slow path for spin locks. > + */ > + if (nr_node_ids > 1 && pv_ops.lock.queued_spin_lock_slowpath == > + native_queued_spin_lock_slowpath) { > + pv_ops.lock.queued_spin_lock_slowpath = > + __cna_queued_spin_lock_slowpath; > + } > +#endif > + > apply_paravirt(__parainstructions, __parainstructions_end); > > restart_nmi(); > diff --git a/kernel/locking/mcs_spinlock.h b/kernel/locking/mcs_spinlock.h > index bc6d3244e1af..36b802babc88 100644 > --- a/kernel/locking/mcs_spinlock.h > +++ b/kernel/locking/mcs_spinlock.h > @@ -17,7 +17,7 @@ > > struct mcs_spinlock { > struct mcs_spinlock *next; > - int locked; /* 1 if lock acquired */ > + u64 locked; /* 1 if lock acquired */ > int count; /* nesting count, see qspinlock.c */ > }; > > diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c > index 5668466b3006..1ba38f85d0ae 100644 > --- a/kernel/locking/qspinlock.c > +++ b/kernel/locking/qspinlock.c > @@ -20,7 +20,7 @@ > * Peter Zijlstra > */ > > -#ifndef _GEN_PV_LOCK_SLOWPATH > +#if !defined(_GEN_PV_LOCK_SLOWPATH) && !defined(_GEN_CNA_LOCK_SLOWPATH) > > #include > #include > @@ -77,18 +77,14 @@ > #define MAX_NODES 4 > > /* > - * On 64-bit architectures, the mcs_spinlock structure will be 16 bytes in > - * size and four of them will fit nicely in one 64-byte cacheline. For > - * pvqspinlock, however, we need more space for extra data. To accommodate > - * that, we insert two more long words to pad it up to 32 bytes. IOW, only > - * two of them can fit in a cacheline in this case. That is OK as it is rare > - * to have more than 2 levels of slowpath nesting in actual use. We don't > - * want to penalize pvqspinlocks to optimize for a rare case in native > - * qspinlocks. > + * On 64-bit architectures, the mcs_spinlock structure will be 20 bytes in > + * size. For pvqspinlock or the NUMA-aware variant, however, we need more > + * space for extra data. To accommodate that, we insert two more long words > + * to pad it up to 36 bytes. > */ The 20 bytes figure is wrong. It is actually 24 bytes for 64-bit as the mcs_spinlock structure is 8-byte aligned. For better cacheline alignment, I will like to keep mcs_spinlock to 16 bytes as before. Instead, you can use encode_tail() to store the CNA node pointer in "locked". For instance, use (encode_tail() << 1) in locked to distinguish it from the regular locked=1 value. > struct qnode { > struct mcs_spinlock mcs; > -#ifdef CONFIG_PARAVIRT_SPINLOCKS > +#if defined(CONFIG_PARAVIRT_SPINLOCKS) || defined(CONFIG_NUMA_AWARE_SPINLOCKS) > long reserved[2]; > #endif > }; > @@ -327,7 +323,7 @@ static __always_inline void __pass_mcs_lock(struct mcs_spinlock *node, > #define set_locked_empty_mcs __set_locked_empty_mcs > #define pass_mcs_lock __pass_mcs_lock > > -#endif /* _GEN_PV_LOCK_SLOWPATH */ > +#endif /* _GEN_PV_LOCK_SLOWPATH && _GEN_CNA_LOCK_SLOWPATH */ > > /** > * queued_spin_lock_slowpath - acquire the queued spinlock > @@ -600,6 +596,29 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val) > EXPORT_SYMBOL(queued_spin_lock_slowpath); > > /* > + * Generate the code for NUMA-aware spin locks > + */ > +#if !defined(_GEN_CNA_LOCK_SLOWPATH) && defined(CONFIG_NUMA_AWARE_SPINLOCKS) > +#define _GEN_CNA_LOCK_SLOWPATH > + > +#undef pv_init_node > +#define pv_init_node cna_init_node > + > +#undef set_locked_empty_mcs > +#define set_locked_empty_mcs cna_set_locked_empty_mcs > + > +#undef pass_mcs_lock > +#define pass_mcs_lock cna_pass_mcs_lock > + > +#undef queued_spin_lock_slowpath > +#define queued_spin_lock_slowpath __cna_queued_spin_lock_slowpath > + > +#include "qspinlock_cna.h" > +#include "qspinlock.c" > + > +#endif > + > +/* > * Generate the paravirt code for queued_spin_unlock_slowpath(). > */ > #if !defined(_GEN_PV_LOCK_SLOWPATH) && defined(CONFIG_PARAVIRT_SPINLOCKS) > diff --git a/kernel/locking/qspinlock_cna.h b/kernel/locking/qspinlock_cna.h > new file mode 100644 > index 000000000000..efb9b12b2f9b > --- /dev/null > +++ b/kernel/locking/qspinlock_cna.h > @@ -0,0 +1,164 @@ > +/* SPDX-License-Identifier: GPL-2.0 */ > +#ifndef _GEN_CNA_LOCK_SLOWPATH > +#error "do not include this file" > +#endif > + > +#include > + > +/* > + * Implement a NUMA-aware version of MCS (aka CNA, or compact NUMA-aware lock). > + * > + * In CNA, spinning threads are organized in two queues, a main queue for > + * threads running on the same node as the current lock holder, and a > + * secondary queue for threads running on other nodes. At the unlock time, > + * the lock holder scans the main queue looking for a thread running on > + * the same node. If found (call it thread T), all threads in the main queue > + * between the current lock holder and T are moved to the end of the > + * secondary queue, and the lock is passed to T. If such T is not found, the > + * lock is passed to the first node in the secondary queue. Finally, if the > + * secondary queue is empty, the lock is passed to the next thread in the > + * main queue. To avoid starvation of threads in the secondary queue, > + * those threads are moved back to the head of the main queue > + * after a certain expected number of intra-node lock hand-offs. > + * > + * For more details, see https://arxiv.org/abs/1810.05600. > + * > + * Authors: Alex Kogan > + * Dave Dice > + */ > + > +struct cna_node { > + struct mcs_spinlock mcs; > + u32 numa_node; > + u32 encoded_tail; > + struct cna_node *tail; /* points to the secondary queue tail */ > +}; > + > +#define CNA_NODE(ptr) ((struct cna_node *)(ptr)) > + > +static void cna_init_node(struct mcs_spinlock *node) > +{ > + struct cna_node *cn = CNA_NODE(node); > + struct mcs_spinlock *base_node; > + int cpuid; > + > + BUILD_BUG_ON(sizeof(struct cna_node) > sizeof(struct qnode)); > + /* we store a pointer in the node's @locked field */ > + BUILD_BUG_ON(sizeof(uintptr_t) > sizeof_field(struct mcs_spinlock, locked)); > + > + cpuid = smp_processor_id(); > + cn->numa_node = cpu_to_node(cpuid); > + > + base_node = this_cpu_ptr(&qnodes[0].mcs); > + cn->encoded_tail = encode_tail(cpuid, base_node->count - 1); > +} I think you can use an early_init call to initialize the numa_node and encoded_tail values for all the per-cpu CNA nodes instead of doing it every time a node is used. If it turns out that pv_qspinlock is used, the pv_node_init() will properly re-initialize it. The only thing left to do here is perhaps setting tail to NULL. -Longman