>From 56b7cfcd417e13b4bfeb77ca290185726c05e69a Mon Sep 17 00:00:00 2001 From: Waiman Long Date: Tue, 28 Jul 2020 12:07:56 -0400 Subject: [PATCH 7/9] locking/qspinlock: Convert to time based spinlock threshold The "numa_spinlock_threshold" kernel command line parameter specifies the number of maximum intra-node lock transfers allowed in a continuously contended lock. Depending on how long the lock critical section lasts, the actual maximum latency can vary quite a lot. Controlling that maximum latency is actually more meaningful than just the number of intra-node lock transfers. By running a locking microbenchmark with null critcal section on a 2-socket x86-64 system, the locking rate was about 4,875 kop/s. The default threshold of 64k translates to about 13ms in intra-node lock transfers. Of course, with a slow critical section, the actual maximum latency will increase substantially. Change the kernel parameter to be time based (in ms) so that the users have a better handle on what maximum latency to expect for inter-node lock transfers. The default is currently set to 10ms. A range of 1-100ms is allowed. That ms value is translated internally to the nearest rounded-up jiffies. Signed-off-by: Waiman Long --- .../admin-guide/kernel-parameters.txt | 13 +++--- kernel/locking/qspinlock_cna.h | 44 +++++++++++++------ 2 files changed, 37 insertions(+), 20 deletions(-) diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 96eb7aae4f63..945e346c678f 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -3339,12 +3339,13 @@ numa_spinlock=auto. numa_spinlock_threshold= [NUMA, PV_OPS] - Set the threshold for the number of intra-node - lock hand-offs before the NUMA-aware spinlock - is forced to be passed to a thread on another NUMA node. - Valid values are in the [0..31] range. Smaller values - result in a more fair, but less performant spinlock, and - vice versa. The default value is 16. + Set the time threshold in milliseconds for the + number of intra-node lock hand-offs before the + NUMA-aware spinlock is forced to be passed to + a thread on another NUMA node. Valid values + are in the [1..100] range. Smaller values result + in a more fair, but less performant spinlock, + and vice versa. The default value is 10. cpu0_hotplug [X86] Turn on CPU0 hotplug feature when CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off. diff --git a/kernel/locking/qspinlock_cna.h b/kernel/locking/qspinlock_cna.h index 911c96279494..03e8ba71a537 100644 --- a/kernel/locking/qspinlock_cna.h +++ b/kernel/locking/qspinlock_cna.h @@ -60,7 +60,7 @@ struct cna_node { u16 real_numa_node; u32 encoded_tail; /* self */ u32 partial_order; /* encoded tail or enum val */ - u32 intra_count; + s32 start_time; }; enum { @@ -70,12 +70,22 @@ enum { }; /* - * Controls the threshold for the number of intra-node lock hand-offs before - * the NUMA-aware variant of spinlock is forced to be passed to a thread on - * another NUMA node. The default setting can be changed with the - * "numa_spinlock_threshold" boot option. + * Controls the threshold time in ms (default = 10) for intra-node lock + * hand-offs before the NUMA-aware variant of spinlock is forced to be + * passed to a thread on another NUMA node. The default setting can be + * changed with the "numa_spinlock_threshold" boot option. */ -unsigned int intra_node_handoff_threshold __ro_after_init = 1 << 16; +#define MSECS_TO_JIFFIES(m) \ + ((m) + (MSEC_PER_SEC / HZ) - 1) / (MSEC_PER_SEC / HZ) +static int intra_node_handoff_threshold __ro_after_init = MSECS_TO_JIFFIES(10); + +static inline bool intra_node_threshold_reached(struct cna_node *cn) +{ + s32 current_time = (s32)jiffies; + s32 threshold = cn->start_time + intra_node_handoff_threshold; + + return current_time - threshold > 0; +} static void __init cna_init_nodes_per_cpu(unsigned int cpu) { @@ -125,7 +135,7 @@ static __always_inline void cna_init_node(struct mcs_spinlock *node) struct cna_node *cn = (struct cna_node *)node; cn->numa_node = priority ? CNA_PRIORITY_NODE : cn->real_numa_node; - cn->intra_count = 0; + cn->start_time = 0; } /* @@ -295,7 +305,14 @@ static __always_inline u32 cna_wait_head_or_lock(struct qspinlock *lock, { struct cna_node *cn = (struct cna_node *)node; - if (cn->intra_count < intra_node_handoff_threshold) { + /* + * In case the previous node passed over the special start_time + * of 0, a refetch of jiffies should be either 0 or 1. + */ + if (!cn->start_time) + cn->start_time = (s32)jiffies; + + if (!intra_node_threshold_reached(cn)) { /* * We are at the head of the wait queue, no need to use * the fake NUMA node ID. @@ -339,8 +356,7 @@ static inline void cna_lock_handoff(struct mcs_spinlock *node, next = node->next; if (node->locked > 1) { val = node->locked; /* preseve secondary queue */ - ((struct cna_node *)next)->intra_count = - cn->intra_count + 1; + ((struct cna_node *)next)->start_time = cn->start_time; } } else if (node->locked > 1) { /* @@ -404,14 +420,14 @@ void __init cna_configure_spin_lock_slowpath(void) static int __init numa_spinlock_threshold_setup(char *str) { - int new_threshold_param; + int param; - if (get_option(&str, &new_threshold_param)) { + if (get_option(&str, ¶m)) { /* valid value is between 0 and 31 */ - if (new_threshold_param < 0 || new_threshold_param > 31) + if (param <= 0 || param > 100) return 0; - intra_node_handoff_threshold = 1 << new_threshold_param; + intra_node_handoff_threshold = msecs_to_jiffies(param); return 1; } -- 2.18.1