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Subject[PATCH 1/1] Drivers: hv: Introduce a policy for controlling channel affinity
Date
From: K. Y. Srinivasan <kys@exchange.microsoft.com>

Introduce a mechanism to control how channels will be affinitized. We will
support two policies:

1. HV_BALANCED: All performance critical channels will be dstributed
evenly amongst all the available NUMA nodes. Once the Node is assigned,
we will assign the CPU based on a simple round robin scheme.

2. HV_LOCALIZED: Only the primary channels are distributed across all
NUMA nodes. Sub-channels will be in the same NUMA node as the primary
channel. This is the current behaviour.

The default policy will be the HV_BALANCED as it can minimize the remote
memory access on NUMA machines with applications that span NUMA nodes.

Signed-off-by: K. Y. Srinivasan <kys@exchange.microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
---
drivers/hv/channel_mgmt.c | 68 +++++++++++++++++++++++++-------------------
include/linux/hyperv.h | 23 +++++++++++++++
2 files changed, 62 insertions(+), 29 deletions(-)

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index 8345869..aaa2c4b 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -338,8 +338,9 @@ void hv_process_channel_removal(struct vmbus_channel *channel, u32 relid)
* We need to free the bit for init_vp_index() to work in the case
* of sub-channel, when we reload drivers like hv_netvsc.
*/
- cpumask_clear_cpu(channel->target_cpu,
- &primary_channel->alloced_cpus_in_node);
+ if (channel->affinity_policy == HV_LOCALIZED)
+ cpumask_clear_cpu(channel->target_cpu,
+ &primary_channel->alloced_cpus_in_node);

free_channel(channel);
}
@@ -524,17 +525,17 @@ static void init_vp_index(struct vmbus_channel *channel, u16 dev_type)
}

/*
- * We distribute primary channels evenly across all the available
- * NUMA nodes and within the assigned NUMA node we will assign the
- * first available CPU to the primary channel.
- * The sub-channels will be assigned to the CPUs available in the
- * NUMA node evenly.
+ * Based on the channel affinity policy, we will assign the NUMA
+ * nodes.
*/
- if (!primary) {
+
+ if ((channel->affinity_policy == HV_BALANCED) || (!primary)) {
while (true) {
next_node = next_numa_node_id++;
- if (next_node == nr_node_ids)
+ if (next_node == nr_node_ids) {
next_node = next_numa_node_id = 0;
+ continue;
+ }
if (cpumask_empty(cpumask_of_node(next_node)))
continue;
break;
@@ -558,15 +559,17 @@ static void init_vp_index(struct vmbus_channel *channel, u16 dev_type)

cur_cpu = -1;

- /*
- * Normally Hyper-V host doesn't create more subchannels than there
- * are VCPUs on the node but it is possible when not all present VCPUs
- * on the node are initialized by guest. Clear the alloced_cpus_in_node
- * to start over.
- */
- if (cpumask_equal(&primary->alloced_cpus_in_node,
- cpumask_of_node(primary->numa_node)))
- cpumask_clear(&primary->alloced_cpus_in_node);
+ if (primary->affinity_policy == HV_LOCALIZED) {
+ /*
+ * Normally Hyper-V host doesn't create more subchannels
+ * than there are VCPUs on the node but it is possible when not
+ * all present VCPUs on the node are initialized by guest.
+ * Clear the alloced_cpus_in_node to start over.
+ */
+ if (cpumask_equal(&primary->alloced_cpus_in_node,
+ cpumask_of_node(primary->numa_node)))
+ cpumask_clear(&primary->alloced_cpus_in_node);
+ }

while (true) {
cur_cpu = cpumask_next(cur_cpu, &available_mask);
@@ -577,17 +580,24 @@ static void init_vp_index(struct vmbus_channel *channel, u16 dev_type)
continue;
}

- /*
- * NOTE: in the case of sub-channel, we clear the sub-channel
- * related bit(s) in primary->alloced_cpus_in_node in
- * hv_process_channel_removal(), so when we reload drivers
- * like hv_netvsc in SMP guest, here we're able to re-allocate
- * bit from primary->alloced_cpus_in_node.
- */
- if (!cpumask_test_cpu(cur_cpu,
- &primary->alloced_cpus_in_node)) {
- cpumask_set_cpu(cur_cpu,
- &primary->alloced_cpus_in_node);
+ if (primary->affinity_policy == HV_LOCALIZED) {
+ /*
+ * NOTE: in the case of sub-channel, we clear the
+ * sub-channel related bit(s) in
+ * primary->alloced_cpus_in_node in
+ * hv_process_channel_removal(), so when we
+ * reload drivers like hv_netvsc in SMP guest, here
+ * we're able to re-allocate
+ * bit from primary->alloced_cpus_in_node.
+ */
+ if (!cpumask_test_cpu(cur_cpu,
+ &primary->alloced_cpus_in_node)) {
+ cpumask_set_cpu(cur_cpu,
+ &primary->alloced_cpus_in_node);
+ cpumask_set_cpu(cur_cpu, alloced_mask);
+ break;
+ }
+ } else {
cpumask_set_cpu(cur_cpu, alloced_mask);
break;
}
diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index 897e4a7..f0f02ec 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -674,6 +674,11 @@ enum hv_signal_policy {
HV_SIGNAL_POLICY_EXPLICIT,
};

+enum hv_numa_policy {
+ HV_BALANCED = 0,
+ HV_LOCALIZED,
+};
+
enum vmbus_device_type {
HV_IDE = 0,
HV_SCSI,
@@ -876,6 +881,18 @@ struct vmbus_channel {
*/
bool low_latency;

+ /*
+ * NUMA distribution policy:
+ * We support teo policies:
+ * 1) Balanced: Here all performance critical channels are
+ * distributed evenly amongst all the NUMA nodes.
+ * This policy will be the default policy.
+ * 2) Localized: All channels of a given instance of a
+ * performance critical service will be assigned CPUs
+ * within a selected NUMA node.
+ */
+ enum hv_numa_policy affinity_policy;
+
};

static inline void set_channel_lock_state(struct vmbus_channel *c, bool state)
@@ -895,6 +912,12 @@ static inline void set_channel_signal_state(struct vmbus_channel *c,
c->signal_policy = policy;
}

+static inline void set_channel_affinity_state(struct vmbus_channel *c,
+ enum hv_numa_policy policy)
+{
+ c->affinity_policy = policy;
+}
+
static inline void set_channel_read_state(struct vmbus_channel *c, bool state)
{
c->batched_reading = state;
--
1.7.4.1
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