From mboxrd@z Thu Jan 1 00:00:00 1970 From: Alex Kogan Subject: [PATCH v5 4/5] locking/qspinlock: Introduce starvation avoidance into CNA Date: Wed, 16 Oct 2019 00:29:02 -0400 Message-ID: <20191016042903.61081-5-alex.kogan@oracle.com> References: <20191016042903.61081-1-alex.kogan@oracle.com> Mime-Version: 1.0 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20191016042903.61081-1-alex.kogan@oracle.com> Sender: linux-kernel-owner@vger.kernel.org To: linux@armlinux.org.uk, peterz@infradead.org, 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, guohanjun@huawei.com, jglauber@marvell.com Cc: steven.sistare@oracle.com, daniel.m.jordan@oracle.com, alex.kogan@oracle.com, dave.dice@oracle.com, rahul.x.yadav@oracle.com List-Id: linux-arch.vger.kernel.org Keep track of the number of intra-node lock handoffs, and force inter-node handoff once this number reaches a preset threshold. Signed-off-by: Alex Kogan Reviewed-by: Steve Sistare --- kernel/locking/qspinlock.c | 3 +++ kernel/locking/qspinlock_cna.h | 30 +++++++++++++++++++++++++++--- 2 files changed, 30 insertions(+), 3 deletions(-) diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index 6d8c4a52e44e..1d0d884308ef 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -597,6 +597,9 @@ EXPORT_SYMBOL(queued_spin_lock_slowpath); #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 pv_wait_head_or_lock #define pv_wait_head_or_lock cna_pre_scan diff --git a/kernel/locking/qspinlock_cna.h b/kernel/locking/qspinlock_cna.h index 4d095f742d31..b92a6f9a19db 100644 --- a/kernel/locking/qspinlock_cna.h +++ b/kernel/locking/qspinlock_cna.h @@ -50,9 +50,19 @@ struct cna_node { struct mcs_spinlock mcs; int numa_node; u32 encoded_tail; - u32 pre_scan_result; /* 0 or an encoded tail */ + u32 pre_scan_result; /* 0, 1 or an encoded tail */ + u32 intra_count; }; +/* + * Controls the threshold for the number of intra-node lock hand-offs. It can + * be tuned and depend, e.g., on the number of CPUs per node. For now, + * choose a value that provides reasonable long-term fairness without + * sacrificing performance compared to a version that does not have any + * fairness guarantees. + */ +#define INTRA_NODE_HANDOFF_THRESHOLD (1 << 16) + static void __init cna_init_nodes_per_cpu(unsigned int cpu) { struct mcs_spinlock *base = per_cpu_ptr(&qnodes[0].mcs, cpu); @@ -86,6 +96,11 @@ static void __init cna_init_nodes(void) } early_initcall(cna_init_nodes); +static __always_inline void cna_init_node(struct mcs_spinlock *node) +{ + ((struct cna_node *)node)->intra_count = 0; +} + static inline bool cna_try_change_tail(struct qspinlock *lock, u32 val, struct mcs_spinlock *node) { @@ -215,7 +230,13 @@ __always_inline u32 cna_pre_scan(struct qspinlock *lock, { struct cna_node *cn = (struct cna_node *)node; - cn->pre_scan_result = cna_scan_main_queue(node, node); + /* + * setting @pre_scan_result to 1 indicates that no post-scan + * should be made in cna_pass_lock() + */ + cn->pre_scan_result = + cn->intra_count == INTRA_NODE_HANDOFF_THRESHOLD ? + 1 : cna_scan_main_queue(node, node); return 0; } @@ -234,7 +255,7 @@ static inline void cna_pass_lock(struct mcs_spinlock *node, * pre-scan, and if so, try to find it in post-scan starting from the * node where pre-scan stopped (stored in @pre_scan_result) */ - if (scan > 0) + if (scan > 1) scan = cna_scan_main_queue(node, decode_tail(scan)); if (!scan) { /* if found a successor from the same numa node */ @@ -245,6 +266,9 @@ static inline void cna_pass_lock(struct mcs_spinlock *node, * to pass the lock */ val = node->locked + (node->locked == 0); + /* inc @intra_count if the secondary queue is not empty */ + ((struct cna_node *)next_holder)->intra_count = + cn->intra_count + (node->locked > 1); } else if (node->locked > 1) { /* if secondary queue is not empty */ /* next holder will be the first node in the secondary queue */ tail_2nd = decode_tail(node->locked); -- 2.11.0 (Apple Git-81) From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from userp2120.oracle.com ([156.151.31.85]:33534 "EHLO userp2120.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2390491AbfJPEcs (ORCPT ); Wed, 16 Oct 2019 00:32:48 -0400 From: Alex Kogan Subject: [PATCH v5 4/5] locking/qspinlock: Introduce starvation avoidance into CNA Date: Wed, 16 Oct 2019 00:29:02 -0400 Message-ID: <20191016042903.61081-5-alex.kogan@oracle.com> In-Reply-To: <20191016042903.61081-1-alex.kogan@oracle.com> References: <20191016042903.61081-1-alex.kogan@oracle.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: linux@armlinux.org.uk, peterz@infradead.org, 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, guohanjun@huawei.com, jglauber@marvell.com Cc: steven.sistare@oracle.com, daniel.m.jordan@oracle.com, alex.kogan@oracle.com, dave.dice@oracle.com, rahul.x.yadav@oracle.com Message-ID: <20191016042902.tjrDI1sPsWyqh5QGjljV-8ywAmO5BlWItn4xk8kCv-U@z> Keep track of the number of intra-node lock handoffs, and force inter-node handoff once this number reaches a preset threshold. Signed-off-by: Alex Kogan Reviewed-by: Steve Sistare --- kernel/locking/qspinlock.c | 3 +++ kernel/locking/qspinlock_cna.h | 30 +++++++++++++++++++++++++++--- 2 files changed, 30 insertions(+), 3 deletions(-) diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c index 6d8c4a52e44e..1d0d884308ef 100644 --- a/kernel/locking/qspinlock.c +++ b/kernel/locking/qspinlock.c @@ -597,6 +597,9 @@ EXPORT_SYMBOL(queued_spin_lock_slowpath); #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 pv_wait_head_or_lock #define pv_wait_head_or_lock cna_pre_scan diff --git a/kernel/locking/qspinlock_cna.h b/kernel/locking/qspinlock_cna.h index 4d095f742d31..b92a6f9a19db 100644 --- a/kernel/locking/qspinlock_cna.h +++ b/kernel/locking/qspinlock_cna.h @@ -50,9 +50,19 @@ struct cna_node { struct mcs_spinlock mcs; int numa_node; u32 encoded_tail; - u32 pre_scan_result; /* 0 or an encoded tail */ + u32 pre_scan_result; /* 0, 1 or an encoded tail */ + u32 intra_count; }; +/* + * Controls the threshold for the number of intra-node lock hand-offs. It can + * be tuned and depend, e.g., on the number of CPUs per node. For now, + * choose a value that provides reasonable long-term fairness without + * sacrificing performance compared to a version that does not have any + * fairness guarantees. + */ +#define INTRA_NODE_HANDOFF_THRESHOLD (1 << 16) + static void __init cna_init_nodes_per_cpu(unsigned int cpu) { struct mcs_spinlock *base = per_cpu_ptr(&qnodes[0].mcs, cpu); @@ -86,6 +96,11 @@ static void __init cna_init_nodes(void) } early_initcall(cna_init_nodes); +static __always_inline void cna_init_node(struct mcs_spinlock *node) +{ + ((struct cna_node *)node)->intra_count = 0; +} + static inline bool cna_try_change_tail(struct qspinlock *lock, u32 val, struct mcs_spinlock *node) { @@ -215,7 +230,13 @@ __always_inline u32 cna_pre_scan(struct qspinlock *lock, { struct cna_node *cn = (struct cna_node *)node; - cn->pre_scan_result = cna_scan_main_queue(node, node); + /* + * setting @pre_scan_result to 1 indicates that no post-scan + * should be made in cna_pass_lock() + */ + cn->pre_scan_result = + cn->intra_count == INTRA_NODE_HANDOFF_THRESHOLD ? + 1 : cna_scan_main_queue(node, node); return 0; } @@ -234,7 +255,7 @@ static inline void cna_pass_lock(struct mcs_spinlock *node, * pre-scan, and if so, try to find it in post-scan starting from the * node where pre-scan stopped (stored in @pre_scan_result) */ - if (scan > 0) + if (scan > 1) scan = cna_scan_main_queue(node, decode_tail(scan)); if (!scan) { /* if found a successor from the same numa node */ @@ -245,6 +266,9 @@ static inline void cna_pass_lock(struct mcs_spinlock *node, * to pass the lock */ val = node->locked + (node->locked == 0); + /* inc @intra_count if the secondary queue is not empty */ + ((struct cna_node *)next_holder)->intra_count = + cn->intra_count + (node->locked > 1); } else if (node->locked > 1) { /* if secondary queue is not empty */ /* next holder will be the first node in the secondary queue */ tail_2nd = decode_tail(node->locked); -- 2.11.0 (Apple Git-81)