On 9/15/20 2:05 PM, Alex Kogan wrote:
Keep track of the time the thread at the head of the secondary queue
has been waiting, and force inter-node handoff once this time passes
a preset threshold. The default value for the threshold (10ms) can be
overridden with the new kernel boot command-line option
"numa_spinlock_threshold". The ms value is translated internally to the
nearest rounded-up jiffies.
Signed-off-by: Alex Kogan <alex.kogan@xxxxxxxxxx>
Reviewed-by: Steve Sistare <steven.sistare@xxxxxxxxxx>
Reviewed-by: Waiman Long <longman@xxxxxxxxxx>
---
.../admin-guide/kernel-parameters.txt | 9 ++
kernel/locking/qspinlock_cna.h | 95 ++++++++++++++++---
2 files changed, 92 insertions(+), 12 deletions(-)
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 51ce050f8701..73ab23a47b97 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -3363,6 +3363,15 @@
Not specifying this option is equivalent to
numa_spinlock=auto.
+ numa_spinlock_threshold= [NUMA, PV_OPS]
+ 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.
Some features depend on CPU0. Known dependencies are:
diff --git a/kernel/locking/qspinlock_cna.h b/kernel/locking/qspinlock_cna.h
index 590402ad69ef..d3e27549c769 100644
--- a/kernel/locking/qspinlock_cna.h
+++ b/kernel/locking/qspinlock_cna.h
@@ -37,6 +37,12 @@
* gradually filter the primary queue, leaving only waiters running on the same
* preferred NUMA node.
*
+ * We change the NUMA node preference after a waiter at the head of the
+ * secondary queue spins for a certain amount of time (10ms, by default).
+ * We do that by flushing the secondary queue into the head of the primary queue,
+ * effectively changing the preference to the NUMA node of the waiter at the head
+ * of the secondary queue at the time of the flush.
+ *
* For more details, see https://arxiv.org/abs/1810.05600.
*
* Authors: Alex Kogan <alex.kogan@xxxxxxxxxx>
@@ -49,13 +55,33 @@ struct cna_node {
u16 real_numa_node;
u32 encoded_tail; /* self */
u32 partial_order; /* enum val */
+ s32 start_time;
};
enum {
LOCAL_WAITER_FOUND,
LOCAL_WAITER_NOT_FOUND,
+ FLUSH_SECONDARY_QUEUE
};
+/*
+ * 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.
+ */
+#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)
{
struct mcs_spinlock *base = per_cpu_ptr(&qnodes[0].mcs, cpu);
@@ -98,6 +124,7 @@ static __always_inline void cna_init_node(struct mcs_spinlock *node)
struct cna_node *cn = (struct cna_node *)node;
cn->numa_node = cn->real_numa_node;
+ cn->start_time = 0;
}
/*
@@ -197,8 +224,15 @@ static void cna_splice_next(struct mcs_spinlock *node,
/* stick `next` on the secondary queue tail */
if (node->locked <= 1) { /* if secondary queue is empty */
+ struct cna_node *cn = (struct cna_node *)node;
+
/* create secondary queue */
next->next = next;
+
+ cn->start_time = (s32)jiffies;
+ /* make sure start_time != 0 iff secondary queue is not empty */
+ if (!cn->start_time)
+ cn->start_time = 1;
My version of the patch set the end_time while yours set the start_time.
The differences are
1) When the node time is 0, yours will reduce the jiffies count by 1. My
version will increase it by 1.
2) The intra_node_handoff_threshold is accessed here in my version when
setting the end time while yours will access it in
intra_node_threshold_reached().
It is largely a matter of preference, but I am just curious about what
you think about the advantage of doing it this way.
Cheers,
Longman
