[RFC PATCH 2/2] Drivers: hv: vmbus: Re-balance channel interrupts across CPUs at device hotplug

Andrea Parri (Microsoft)
2020-05-26T22:33:10Z

Device hot removals and additions (closure and opening) also present a
valid opportunity for (re-)balancing the channel interrupts across the
available CPUs. Current code balances interrupts as they are offered,
but it does not modify the interrupts-to-CPUs assignment if interrupts
are "rescinded"/removed from the system. Moreover, in case of channel
/device offers, the interrupt assignments are performed *one at a time*
and without full visibility into other channels/devices; the result is
that, globally, interrupts are sometimes not evenly spread across CPUs.

Introduce the vmbus_balance_vp_indexes_at_devhp() primitive to balance
the channel interrupts across online CPUs at device hotplug operations.
The primitive triggers a "full" balancing of the interrupts across the
online CPUs and NUMA nodes. The balancing process at device addition/
opening is deferred to a delayed work, to give channels of such device
more chances to be opened. As in vmbus_balance_vp_indexes_at_cpuhp(),
the balancing is applied to "performance" channels only, and it relies
on the (new) capability to re-assign a channel interrupt.

Suggested-by: Nuno Das Neves <nuno.das@microsoft.com>
Signed-off-by: Andrea Parri (Microsoft) <parri.andrea@gmail.com>
---
drivers/hv/channel.c | 43 ++++++++++++++++++++++++++++++++
drivers/hv/channel_mgmt.c | 52 ++++++++++++++++++++++++++++++++++++---
drivers/hv/connection.c | 9 +++++++
drivers/hv/hyperv_vmbus.h | 6 +++++
include/linux/hyperv.h | 6 +++++
5 files changed, 112 insertions(+), 4 deletions(-)

diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c
index 2974aa9dc956c..076f2d68a1efe 100644
--- a/drivers/hv/channel.c
+++ b/drivers/hv/channel.c
@@ -11,6 +11,7 @@
#include <linux/kernel.h>
#include <linux/sched.h>
#include <linux/wait.h>
+#include <linux/cpu.h>
#include <linux/mm.h>
#include <linux/slab.h>
#include <linux/module.h>
@@ -112,6 +113,19 @@ int vmbus_alloc_ring(struct vmbus_channel *newchannel,
}
EXPORT_SYMBOL_GPL(vmbus_alloc_ring);

+static void vmbus_add_device_work(struct work_struct *work)
+{
+ struct hv_device *hv_dev =
+ container_of((struct delayed_work *)work, struct hv_device,
+ add_device_work);
+
+ cpus_read_lock();
+ mutex_lock(&vmbus_connection.channel_mutex);
+ vmbus_balance_vp_indexes_at_devhp(hv_dev, true);
+ mutex_unlock(&vmbus_connection.channel_mutex);
+ cpus_read_unlock();
+}
+
static int __vmbus_open(struct vmbus_channel *newchannel,
void *userdata, u32 userdatalen,
void (*onchannelcallback)(void *context), void *context)
@@ -217,6 +231,24 @@ static int __vmbus_open(struct vmbus_channel *newchannel,
}

newchannel->state = CHANNEL_OPENED_STATE;
+ /*
+ * If this is a primary channel and a "perf" channel, queue the
+ * add_device_work to balance the channels of the device across
+ * the online CPUs; the queueing delay should be greater than
+ * the "typical" time required to open such channels, since the
+ * balancing will only apply to *open* channels. The closure
+ * path will wait for our work to complete and start a new re-
+ * balancing, cf. vmbus_disconnect_ring().
+ */
+ if (newchannel->primary_channel == NULL &&
+ hv_is_perf_channel(newchannel)) {
+ struct delayed_work *dwork =
+ &newchannel->device_obj->add_device_work;
+
+ INIT_DELAYED_WORK(dwork, vmbus_add_device_work);
+ queue_delayed_work(vmbus_connection.handle_dev_wq, dwork,
+ 8 * HZ);
+ }
kfree(open_info);
return 0;

@@ -750,6 +782,8 @@ static int vmbus_close_internal(struct vmbus_channel *channel)
/* disconnect ring - close all channels */
int vmbus_disconnect_ring(struct vmbus_channel *channel)
{
+ struct hv_device *hv_dev = channel->device_obj;
+ bool perf_chn = hv_is_perf_channel(channel);
struct vmbus_channel *cur_channel, *tmp;
int ret;

@@ -773,9 +807,18 @@ int vmbus_disconnect_ring(struct vmbus_channel *channel)
/*
* Now close the primary.
*/
+
+ /* See inline comment in __vmbus_open(). */
+ if (perf_chn)
+ cancel_delayed_work_sync(&hv_dev->add_device_work);
+
+ cpus_read_lock();
mutex_lock(&vmbus_connection.channel_mutex);
+ if (perf_chn)
+ vmbus_balance_vp_indexes_at_devhp(hv_dev, false);
ret = vmbus_close_internal(channel);
mutex_unlock(&vmbus_connection.channel_mutex);
+ cpus_read_unlock();

return ret;
}
diff --git a/drivers/hv/channel_mgmt.c b/drivers/hv/channel_mgmt.c
index c158f86787940..91b1bd2914d79 100644
--- a/drivers/hv/channel_mgmt.c
+++ b/drivers/hv/channel_mgmt.c
@@ -815,6 +815,49 @@ static void balance_vp_index(struct vmbus_channel *chn,
inc_chn_counts(&vmbus_connection.chn_cnt, tgt_cpu);
}

+void vmbus_balance_vp_indexes_at_devhp(struct hv_device *hv_dev, bool add)
+{
+ struct vmbus_channel *chn, *sc;
+ cpumask_var_t cpu_msk;
+
+ lockdep_assert_cpus_held();
+ lockdep_assert_held(&vmbus_connection.channel_mutex);
+
+ WARN_ON(!hv_is_perf_channel(hv_dev->channel));
+
+ /* See the header comment for vmbus_send_modifychannel(). */
+ if (vmbus_proto_version < VERSION_WIN10_V4_1)
+ return;
+
+ if (!alloc_cpumask_var(&cpu_msk, GFP_KERNEL))
+ return;
+
+ reset_chn_counts(&vmbus_connection.chn_cnt);
+
+ list_for_each_entry(chn, &vmbus_connection.chn_list, listentry) {
+ struct hv_device *dev = chn->device_obj;
+
+ /* See comment in vmbus_balance_vp_indexes_at_cpuhp(). */
+ if (!hv_is_perf_channel(chn) || dev == NULL)
+ continue;
+
+ if (dev == hv_dev && !add)
+ continue;
+
+ reset_chn_counts(&dev->chn_cnt);
+
+ cpumask_copy(cpu_msk, cpu_online_mask);
+ balance_vp_index(chn, dev, cpu_msk);
+
+ list_for_each_entry(sc, &chn->sc_list, sc_list) {
+ cpumask_copy(cpu_msk, cpu_online_mask);
+ balance_vp_index(sc, dev, cpu_msk);
+ }
+ }
+
+ free_cpumask_var(cpu_msk);
+}
+
void vmbus_balance_vp_indexes_at_cpuhp(unsigned int cpu, bool add)
{
struct vmbus_channel *chn, *sc;
@@ -840,10 +883,11 @@ void vmbus_balance_vp_indexes_at_cpuhp(unsigned int cpu, bool add)
/*
* The device may not have been allocated/assigned to
* the primary channel yet; if so, do not balance the
- * channels associated to this device. If dev != NULL,
- * the synchronization on channel_mutex ensures that
- * the device's chn_cnt has been (properly) allocated
- * *and* initialized, cf. vmbus_add_channel_work().
+ * channels associated to the device and "defer" this
+ * to vmbus_balance_vp_indexes_at_devhp(). If dev !=
+ * NULL, the synchronization on channel_mutex ensures
+ * that the device's chn_cnt has been allocated *and*
+ * initialized, cf. vmbus_add_channel_work().
*/
if (dev == NULL)
continue;
diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
index 7ec562fac8e58..f93060babd9a4 100644
--- a/drivers/hv/connection.c
+++ b/drivers/hv/connection.c
@@ -179,6 +179,12 @@ int vmbus_connect(void)
goto cleanup;
}

+ vmbus_connection.handle_dev_wq = create_workqueue("hv_device");
+ if (!vmbus_connection.handle_dev_wq) {
+ ret = -ENOMEM;
+ goto cleanup;
+ }
+
INIT_LIST_HEAD(&vmbus_connection.chn_msg_list);
spin_lock_init(&vmbus_connection.channelmsg_lock);

@@ -281,6 +287,9 @@ void vmbus_disconnect(void)
*/
vmbus_initiate_unload(false);

+ if (vmbus_connection.handle_dev_wq)
+ destroy_workqueue(vmbus_connection.handle_dev_wq);
+
if (vmbus_connection.handle_sub_chan_wq)
destroy_workqueue(vmbus_connection.handle_sub_chan_wq);

diff --git a/drivers/hv/hyperv_vmbus.h b/drivers/hv/hyperv_vmbus.h
index b6d194caf69ed..b461cf7efd91c 100644
--- a/drivers/hv/hyperv_vmbus.h
+++ b/drivers/hv/hyperv_vmbus.h
@@ -272,6 +272,11 @@ struct vmbus_connection {
struct workqueue_struct *work_queue;
struct workqueue_struct *handle_primary_chan_wq;
struct workqueue_struct *handle_sub_chan_wq;
+ /*
+ * Handling device hotplug/addition work, cf. add_device_work from
+ * struct hv_device.
+ */
+ struct workqueue_struct *handle_dev_wq;

/*
* The number of sub-channels and hv_sock channels that should be
@@ -358,6 +363,7 @@ struct vmbus_channel *relid2channel(u32 relid);

void vmbus_free_channels(void);

+void vmbus_balance_vp_indexes_at_devhp(struct hv_device *hv_dev, bool add);
void vmbus_balance_vp_indexes_at_cpuhp(unsigned int cpu, bool add);

/* Connection interface */
diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
index 0e9f695ea8f87..ce0bf3001792f 100644
--- a/include/linux/hyperv.h
+++ b/include/linux/hyperv.h
@@ -1212,6 +1212,12 @@ struct hv_device {

/* place holder to keep track of the dir for hv device in debugfs */
struct dentry *debug_dir;
+
+ /*
+ * Balance the channel interrupts across the online CPUs at device
+ * hotplug/addition.
+ */
+ struct delayed_work add_device_work;
};

--
2.25.1