From: Alex Kogan <alex.kogan@oracle.com>
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
Subject: [PATCH v5 4/5] locking/qspinlock: Introduce starvation avoidance into CNA
Date: Wed, 16 Oct 2019 00:29:02 -0400 [thread overview]
Message-ID: <20191016042903.61081-5-alex.kogan@oracle.com> (raw)
In-Reply-To: <20191016042903.61081-1-alex.kogan@oracle.com>
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 <alex.kogan@oracle.com>
Reviewed-by: Steve Sistare <steven.sistare@oracle.com>
---
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)
next prev parent reply other threads:[~2019-10-16 4:32 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-10-16 4:28 [PATCH v5 0/5] Add NUMA-awareness to qspinlock Alex Kogan
2019-10-16 4:28 ` [PATCH v5 1/5] locking/qspinlock: Rename mcs lock/unlock macros and make them more generic Alex Kogan
2019-10-16 4:29 ` [PATCH v5 2/5] locking/qspinlock: Refactor the qspinlock slow path Alex Kogan
2019-10-16 4:29 ` [PATCH v5 3/5] locking/qspinlock: Introduce CNA into the slow path of qspinlock Alex Kogan
2019-10-16 20:57 ` Waiman Long
2019-10-18 19:48 ` Alex Kogan
2019-10-18 16:03 ` Waiman Long
2019-10-18 21:37 ` Alex Kogan
2019-10-18 21:55 ` Waiman Long
2019-10-16 4:29 ` Alex Kogan [this message]
2019-10-18 16:09 ` [PATCH v5 4/5] locking/qspinlock: Introduce starvation avoidance into CNA Waiman Long
2019-10-16 4:29 ` [PATCH v5 5/5] locking/qspinlock: Introduce the shuffle reduction optimization " Alex Kogan
2019-10-18 16:19 ` [PATCH v5 0/5] Add NUMA-awareness to qspinlock Waiman Long
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