[PATCH 1/1] drm/amdkfd: Improve concurrency of event handling
Keely, Sean
Sean.Keely at amd.com
Wed Mar 2 22:53:15 UTC 2022
[AMD Official Use Only]
LGTM.
Reviewed-by: Sean Keely <Sean.Keely at amd.com>
-----Original Message-----
From: Kuehling, Felix <Felix.Kuehling at amd.com>
Sent: Wednesday, March 02, 2022 2:06 PM
To: amd-gfx at lists.freedesktop.org
Cc: Keely, Sean <Sean.Keely at amd.com>
Subject: [PATCH 1/1] drm/amdkfd: Improve concurrency of event handling
Use rcu_read_lock to read p->event_idr concurrently with other readers
and writers. Use p->event_mutex only for creating and destroying events
and in kfd_wait_on_events.
Protect the contents of the kfd_event structure with a per-event
spinlock that can be taken inside the rcu_read_lock critical section.
This eliminates contention of p->event_mutex in set_event, which tends
to be on the critical path for dispatch latency even when busy waiting
is used. It also eliminates lock contention in event interrupt handlers.
Since the p->event_mutex is now used much less, the impact of requiring
it in kfd_wait_on_events should also be much smaller.
This should improve event handling latency for processes using multiple
GPUs concurrently.
Signed-off-by: Felix Kuehling <Felix.Kuehling at amd.com>
---
drivers/gpu/drm/amd/amdkfd/kfd_events.c | 119 +++++++++++++++---------
drivers/gpu/drm/amd/amdkfd/kfd_events.h | 1 +
2 files changed, 78 insertions(+), 42 deletions(-)
diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_events.c b/drivers/gpu/drm/amd/amdkfd/kfd_events.c
index deecccebe5b6..1726306715b2 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_events.c
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_events.c
@@ -128,8 +128,8 @@ static int allocate_event_notification_slot(struct kfd_process *p,
}
/*
- * Assumes that p->event_mutex is held and of course that p is not going
- * away (current or locked).
+ * Assumes that p->event_mutex or rcu_readlock is held and of course that p is
+ * not going away.
*/
static struct kfd_event *lookup_event_by_id(struct kfd_process *p, uint32_t id)
{
@@ -251,15 +251,18 @@ static void destroy_event(struct kfd_process *p, struct kfd_event *ev)
struct kfd_event_waiter *waiter;
/* Wake up pending waiters. They will return failure */
+ spin_lock(&ev->lock);
list_for_each_entry(waiter, &ev->wq.head, wait.entry)
- waiter->event = NULL;
+ WRITE_ONCE(waiter->event, NULL);
wake_up_all(&ev->wq);
+ spin_unlock(&ev->lock);
if (ev->type == KFD_EVENT_TYPE_SIGNAL ||
ev->type == KFD_EVENT_TYPE_DEBUG)
p->signal_event_count--;
idr_remove(&p->event_idr, ev->event_id);
+ synchronize_rcu();
kfree(ev);
}
@@ -392,6 +395,7 @@ int kfd_event_create(struct file *devkfd, struct kfd_process *p,
ev->auto_reset = auto_reset;
ev->signaled = false;
+ spin_lock_init(&ev->lock);
init_waitqueue_head(&ev->wq);
*event_page_offset = 0;
@@ -466,6 +470,7 @@ int kfd_criu_restore_event(struct file *devkfd,
ev->auto_reset = ev_priv->auto_reset;
ev->signaled = ev_priv->signaled;
+ spin_lock_init(&ev->lock);
init_waitqueue_head(&ev->wq);
mutex_lock(&p->event_mutex);
@@ -609,13 +614,13 @@ static void set_event(struct kfd_event *ev)
/* Auto reset if the list is non-empty and we're waking
* someone. waitqueue_active is safe here because we're
- * protected by the p->event_mutex, which is also held when
+ * protected by the ev->lock, which is also held when
* updating the wait queues in kfd_wait_on_events.
*/
ev->signaled = !ev->auto_reset || !waitqueue_active(&ev->wq);
list_for_each_entry(waiter, &ev->wq.head, wait.entry)
- waiter->activated = true;
+ WRITE_ONCE(waiter->activated, true);
wake_up_all(&ev->wq);
}
@@ -626,16 +631,18 @@ int kfd_set_event(struct kfd_process *p, uint32_t event_id)
int ret = 0;
struct kfd_event *ev;
- mutex_lock(&p->event_mutex);
+ rcu_read_lock();
ev = lookup_event_by_id(p, event_id);
+ spin_lock(&ev->lock);
if (ev && event_can_be_cpu_signaled(ev))
set_event(ev);
else
ret = -EINVAL;
- mutex_unlock(&p->event_mutex);
+ spin_unlock(&ev->lock);
+ rcu_read_unlock();
return ret;
}
@@ -650,23 +657,25 @@ int kfd_reset_event(struct kfd_process *p, uint32_t event_id)
int ret = 0;
struct kfd_event *ev;
- mutex_lock(&p->event_mutex);
+ rcu_read_lock();
ev = lookup_event_by_id(p, event_id);
+ spin_lock(&ev->lock);
if (ev && event_can_be_cpu_signaled(ev))
reset_event(ev);
else
ret = -EINVAL;
- mutex_unlock(&p->event_mutex);
+ spin_unlock(&ev->lock);
+ rcu_read_unlock();
return ret;
}
static void acknowledge_signal(struct kfd_process *p, struct kfd_event *ev)
{
- page_slots(p->signal_page)[ev->event_id] = UNSIGNALED_EVENT_SLOT;
+ WRITE_ONCE(page_slots(p->signal_page)[ev->event_id], UNSIGNALED_EVENT_SLOT);
}
static void set_event_from_interrupt(struct kfd_process *p,
@@ -674,7 +683,9 @@ static void set_event_from_interrupt(struct kfd_process *p,
{
if (ev && event_can_be_gpu_signaled(ev)) {
acknowledge_signal(p, ev);
+ spin_lock(&ev->lock);
set_event(ev);
+ spin_unlock(&ev->lock);
}
}
@@ -693,7 +704,7 @@ void kfd_signal_event_interrupt(u32 pasid, uint32_t partial_id,
if (!p)
return; /* Presumably process exited. */
- mutex_lock(&p->event_mutex);
+ rcu_read_lock();
if (valid_id_bits)
ev = lookup_signaled_event_by_partial_id(p, partial_id,
@@ -721,7 +732,7 @@ void kfd_signal_event_interrupt(u32 pasid, uint32_t partial_id,
if (id >= KFD_SIGNAL_EVENT_LIMIT)
break;
- if (slots[id] != UNSIGNALED_EVENT_SLOT)
+ if (READ_ONCE(slots[id]) != UNSIGNALED_EVENT_SLOT)
set_event_from_interrupt(p, ev);
}
} else {
@@ -730,14 +741,14 @@ void kfd_signal_event_interrupt(u32 pasid, uint32_t partial_id,
* only signaled events from the IDR.
*/
for (id = 0; id < KFD_SIGNAL_EVENT_LIMIT; id++)
- if (slots[id] != UNSIGNALED_EVENT_SLOT) {
+ if (READ_ONCE(slots[id]) != UNSIGNALED_EVENT_SLOT) {
ev = lookup_event_by_id(p, id);
set_event_from_interrupt(p, ev);
}
}
}
- mutex_unlock(&p->event_mutex);
+ rcu_read_unlock();
kfd_unref_process(p);
}
@@ -767,9 +778,11 @@ static int init_event_waiter_get_status(struct kfd_process *p,
if (!ev)
return -EINVAL;
+ spin_lock(&ev->lock);
waiter->event = ev;
waiter->activated = ev->signaled;
ev->signaled = ev->signaled && !ev->auto_reset;
+ spin_unlock(&ev->lock);
return 0;
}
@@ -781,8 +794,11 @@ static void init_event_waiter_add_to_waitlist(struct kfd_event_waiter *waiter)
/* Only add to the wait list if we actually need to
* wait on this event.
*/
- if (!waiter->activated)
+ if (!waiter->activated) {
+ spin_lock(&ev->lock);
add_wait_queue(&ev->wq, &waiter->wait);
+ spin_unlock(&ev->lock);
+ }
}
/* test_event_condition - Test condition of events being waited for
@@ -802,10 +818,10 @@ static uint32_t test_event_condition(bool all, uint32_t num_events,
uint32_t activated_count = 0;
for (i = 0; i < num_events; i++) {
- if (!event_waiters[i].event)
+ if (!READ_ONCE(event_waiters[i].event))
return KFD_IOC_WAIT_RESULT_FAIL;
- if (event_waiters[i].activated) {
+ if (READ_ONCE(event_waiters[i].activated)) {
if (!all)
return KFD_IOC_WAIT_RESULT_COMPLETE;
@@ -834,6 +850,8 @@ static int copy_signaled_event_data(uint32_t num_events,
for (i = 0; i < num_events; i++) {
waiter = &event_waiters[i];
event = waiter->event;
+ if (!event)
+ return -EINVAL; /* event was destroyed */
if (waiter->activated && event->type == KFD_EVENT_TYPE_MEMORY) {
dst = &data[i].memory_exception_data;
src = &event->memory_exception_data;
@@ -844,11 +862,8 @@ static int copy_signaled_event_data(uint32_t num_events,
}
return 0;
-
}
-
-
static long user_timeout_to_jiffies(uint32_t user_timeout_ms)
{
if (user_timeout_ms == KFD_EVENT_TIMEOUT_IMMEDIATE)
@@ -872,9 +887,12 @@ static void free_waiters(uint32_t num_events, struct kfd_event_waiter *waiters)
uint32_t i;
for (i = 0; i < num_events; i++)
- if (waiters[i].event)
+ if (waiters[i].event) {
+ spin_lock(&waiters[i].event->lock);
remove_wait_queue(&waiters[i].event->wq,
&waiters[i].wait);
+ spin_unlock(&waiters[i].event->lock);
+ }
kfree(waiters);
}
@@ -898,6 +916,9 @@ int kfd_wait_on_events(struct kfd_process *p,
goto out;
}
+ /* Use p->event_mutex here to protect against concurrent creation and
+ * destruction of events while we initialize event_waiters.
+ */
mutex_lock(&p->event_mutex);
for (i = 0; i < num_events; i++) {
@@ -976,14 +997,19 @@ int kfd_wait_on_events(struct kfd_process *p,
}
__set_current_state(TASK_RUNNING);
+ mutex_lock(&p->event_mutex);
/* copy_signaled_event_data may sleep. So this has to happen
* after the task state is set back to RUNNING.
+ *
+ * The event may also have been destroyed after signaling. So
+ * copy_signaled_event_data also must confirm that the event
+ * still exists. Therefore this must be under the p->event_mutex
+ * which is also held when events are destroyed.
*/
if (!ret && *wait_result == KFD_IOC_WAIT_RESULT_COMPLETE)
ret = copy_signaled_event_data(num_events,
event_waiters, events);
- mutex_lock(&p->event_mutex);
out_unlock:
free_waiters(num_events, event_waiters);
mutex_unlock(&p->event_mutex);
@@ -1042,8 +1068,7 @@ int kfd_event_mmap(struct kfd_process *p, struct vm_area_struct *vma)
}
/*
- * Assumes that p->event_mutex is held and of course
- * that p is not going away (current or locked).
+ * Assumes that p is not going away.
*/
static void lookup_events_by_type_and_signal(struct kfd_process *p,
int type, void *event_data)
@@ -1055,6 +1080,8 @@ static void lookup_events_by_type_and_signal(struct kfd_process *p,
ev_data = (struct kfd_hsa_memory_exception_data *) event_data;
+ rcu_read_lock();
+
id = KFD_FIRST_NONSIGNAL_EVENT_ID;
idr_for_each_entry_continue(&p->event_idr, ev, id)
if (ev->type == type) {
@@ -1062,9 +1089,11 @@ static void lookup_events_by_type_and_signal(struct kfd_process *p,
dev_dbg(kfd_device,
"Event found: id %X type %d",
ev->event_id, ev->type);
+ spin_lock(&ev->lock);
set_event(ev);
if (ev->type == KFD_EVENT_TYPE_MEMORY && ev_data)
ev->memory_exception_data = *ev_data;
+ spin_unlock(&ev->lock);
}
if (type == KFD_EVENT_TYPE_MEMORY) {
@@ -1087,6 +1116,8 @@ static void lookup_events_by_type_and_signal(struct kfd_process *p,
p->lead_thread->pid, p->pasid);
}
}
+
+ rcu_read_unlock();
}
#ifdef KFD_SUPPORT_IOMMU_V2
@@ -1162,16 +1193,10 @@ void kfd_signal_iommu_event(struct kfd_dev *dev, u32 pasid,
if (KFD_GC_VERSION(dev) != IP_VERSION(9, 1, 0) &&
KFD_GC_VERSION(dev) != IP_VERSION(9, 2, 2) &&
- KFD_GC_VERSION(dev) != IP_VERSION(9, 3, 0)) {
- mutex_lock(&p->event_mutex);
-
- /* Lookup events by type and signal them */
+ KFD_GC_VERSION(dev) != IP_VERSION(9, 3, 0))
lookup_events_by_type_and_signal(p, KFD_EVENT_TYPE_MEMORY,
&memory_exception_data);
- mutex_unlock(&p->event_mutex);
- }
-
kfd_unref_process(p);
}
#endif /* KFD_SUPPORT_IOMMU_V2 */
@@ -1188,12 +1213,7 @@ void kfd_signal_hw_exception_event(u32 pasid)
if (!p)
return; /* Presumably process exited. */
- mutex_lock(&p->event_mutex);
-
- /* Lookup events by type and signal them */
lookup_events_by_type_and_signal(p, KFD_EVENT_TYPE_HW_EXCEPTION, NULL);
-
- mutex_unlock(&p->event_mutex);
kfd_unref_process(p);
}
@@ -1229,16 +1249,19 @@ void kfd_signal_vm_fault_event(struct kfd_dev *dev, u32 pasid,
info->prot_write ? 1 : 0;
memory_exception_data.failure.imprecise = 0;
}
- mutex_lock(&p->event_mutex);
+
+ rcu_read_lock();
id = KFD_FIRST_NONSIGNAL_EVENT_ID;
idr_for_each_entry_continue(&p->event_idr, ev, id)
if (ev->type == KFD_EVENT_TYPE_MEMORY) {
+ spin_lock(&ev->lock);
ev->memory_exception_data = memory_exception_data;
set_event(ev);
+ spin_unlock(&ev->lock);
}
- mutex_unlock(&p->event_mutex);
+ rcu_read_unlock();
kfd_unref_process(p);
}
@@ -1272,22 +1295,28 @@ void kfd_signal_reset_event(struct kfd_dev *dev)
continue;
}
- mutex_lock(&p->event_mutex);
+ rcu_read_lock();
+
id = KFD_FIRST_NONSIGNAL_EVENT_ID;
idr_for_each_entry_continue(&p->event_idr, ev, id) {
if (ev->type == KFD_EVENT_TYPE_HW_EXCEPTION) {
+ spin_lock(&ev->lock);
ev->hw_exception_data = hw_exception_data;
ev->hw_exception_data.gpu_id = user_gpu_id;
set_event(ev);
+ spin_unlock(&ev->lock);
}
if (ev->type == KFD_EVENT_TYPE_MEMORY &&
reset_cause == KFD_HW_EXCEPTION_ECC) {
+ spin_lock(&ev->lock);
ev->memory_exception_data = memory_exception_data;
ev->memory_exception_data.gpu_id = user_gpu_id;
set_event(ev);
+ spin_unlock(&ev->lock);
}
}
- mutex_unlock(&p->event_mutex);
+
+ rcu_read_unlock();
}
srcu_read_unlock(&kfd_processes_srcu, idx);
}
@@ -1320,19 +1349,25 @@ void kfd_signal_poison_consumed_event(struct kfd_dev *dev, u32 pasid)
memory_exception_data.gpu_id = user_gpu_id;
memory_exception_data.failure.imprecise = true;
- mutex_lock(&p->event_mutex);
+ rcu_read_lock();
+
idr_for_each_entry_continue(&p->event_idr, ev, id) {
if (ev->type == KFD_EVENT_TYPE_HW_EXCEPTION) {
+ spin_lock(&ev->lock);
ev->hw_exception_data = hw_exception_data;
set_event(ev);
+ spin_unlock(&ev->lock);
}
if (ev->type == KFD_EVENT_TYPE_MEMORY) {
+ spin_lock(&ev->lock);
ev->memory_exception_data = memory_exception_data;
set_event(ev);
+ spin_unlock(&ev->lock);
}
}
- mutex_unlock(&p->event_mutex);
+
+ rcu_read_unlock();
/* user application will handle SIGBUS signal */
send_sig(SIGBUS, p->lead_thread, 0);
diff --git a/drivers/gpu/drm/amd/amdkfd/kfd_events.h b/drivers/gpu/drm/amd/amdkfd/kfd_events.h
index 1238af11916e..55d376f56021 100644
--- a/drivers/gpu/drm/amd/amdkfd/kfd_events.h
+++ b/drivers/gpu/drm/amd/amdkfd/kfd_events.h
@@ -59,6 +59,7 @@ struct kfd_event {
int type;
+ spinlock_t lock;
wait_queue_head_t wq; /* List of event waiters. */
/* Only for signal events. */
--
2.32.0
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