Drivers: hv: Introduce a policy for controlling channel affinity

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@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index d8b64ba..bbd812e 100644 (file)
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -356,8 +356,9 @@ 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);
 
        vmbus_release_relid(relid);
 
@@ -548,17 +549,17 @@ 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;
@@ -582,15 +583,17 @@ 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);
@@ -601,17 +604,24 @@ 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 e6ef571..c877e79 100644 (file)
--- 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;