In V3D, the conclusion of a job is indicated by a IRQ. When a job
finishes, then we update the local and the global GPU stats of that
queue. But, while the GPU stats are being updated, a user might be
reading the stats from sysfs or fdinfo.
For example, on `gpu_stats_show()`, we could think about a scenario where
`v3d->queue[queue].start_ns != 0`, then an interruption happens, we update
the value of `v3d->queue[queue].start_ns` to 0, we come back to `gpu_stats_show()`
to calculate `active_runtime` and now, `active_runtime = timestamp`.
In this simple example, the user would see a spike in the queue usage,
that didn't matches reality.
In order to address this issue properly, use rw-locks to protect read
and write sections of the code.
Fixes: 09a93cc4f7d1 ("drm/v3d: Implement show_fdinfo() callback for GPU usage stats")
Reported-by: Tvrtko Ursulin <tursulin@xxxxxxxxxx>
Signed-off-by: Maíra Canal <mcanal@xxxxxxxxxx>
---
drivers/gpu/drm/v3d/v3d_drv.c | 16 ++++++++++++----
drivers/gpu/drm/v3d/v3d_drv.h | 7 +++++++
drivers/gpu/drm/v3d/v3d_gem.c | 7 +++++--
drivers/gpu/drm/v3d/v3d_sched.c | 9 +++++++++
drivers/gpu/drm/v3d/v3d_sysfs.c | 16 ++++++++--------
5 files changed, 41 insertions(+), 14 deletions(-)
diff --git a/drivers/gpu/drm/v3d/v3d_drv.c b/drivers/gpu/drm/v3d/v3d_drv.c
index cbb62be18aa5..60437718786c 100644
--- a/drivers/gpu/drm/v3d/v3d_drv.c
+++ b/drivers/gpu/drm/v3d/v3d_drv.c
@@ -119,7 +119,9 @@ v3d_open(struct drm_device *dev, struct drm_file *file)
drm_sched_entity_init(&v3d_priv->sched_entity[i],
DRM_SCHED_PRIORITY_NORMAL, &sched,
1, NULL);
+
memset(&v3d_priv->stats[i], 0, sizeof(v3d_priv->stats[i]));
+ rwlock_init(&v3d_priv->stats[i].rw_lock);
}
v3d_perfmon_open_file(v3d_priv);
@@ -149,20 +151,26 @@ static void v3d_show_fdinfo(struct drm_printer *p, struct drm_file *file)
for (queue = 0; queue < V3D_MAX_QUEUES; queue++) {
struct v3d_stats *stats = &file_priv->stats[queue];
+ u64 active_time, jobs_sent;
+ unsigned long flags;
+
+ read_lock_irqsave(&stats->rw_lock, flags);
+ active_time = stats->start_ns ? stats->enabled_ns + timestamp - stats->start_ns
+ : stats->enabled_ns;
+ jobs_sent = stats->jobs_sent;
+ read_unlock_irqrestore(&stats->rw_lock, flags);
/* Note that, in case of a GPU reset, the time spent during an
* attempt of executing the job is not computed in the runtime.
*/
drm_printf(p, "drm-engine-%s: \t%llu ns\n",
- v3d_queue_to_string(queue),
- stats->start_ns ? stats->enabled_ns + timestamp - stats->start_ns
- : stats->enabled_ns);
+ v3d_queue_to_string(queue), active_time);
/* Note that we only count jobs that completed. Therefore, jobs
* that were resubmitted due to a GPU reset are not computed.
*/
drm_printf(p, "v3d-jobs-%s: \t%llu jobs\n",
- v3d_queue_to_string(queue), stats->jobs_sent);
+ v3d_queue_to_string(queue), jobs_sent);
}
}
diff --git a/drivers/gpu/drm/v3d/v3d_drv.h b/drivers/gpu/drm/v3d/v3d_drv.h
index 0117593976ed..8fde2623f763 100644
--- a/drivers/gpu/drm/v3d/v3d_drv.h
+++ b/drivers/gpu/drm/v3d/v3d_drv.h
@@ -40,6 +40,13 @@ struct v3d_stats {
u64 start_ns;
u64 enabled_ns;
u64 jobs_sent;
+
+ /*
+ * This lock is used to protect the access to the GPU stats variables.
+ * It must be used as, while we are reading the stats, IRQs can happen
+ * and the stats would be updated.
+ */
+ rwlock_t rw_lock;
};
struct v3d_queue_state {
diff --git a/drivers/gpu/drm/v3d/v3d_gem.c b/drivers/gpu/drm/v3d/v3d_gem.c
index d14589d3ae6c..439088724a51 100644
--- a/drivers/gpu/drm/v3d/v3d_gem.c
+++ b/drivers/gpu/drm/v3d/v3d_gem.c
@@ -247,8 +247,11 @@ v3d_gem_init(struct drm_device *dev)
int ret, i;
for (i = 0; i < V3D_MAX_QUEUES; i++) {
- v3d->queue[i].fence_context = dma_fence_context_alloc(1);
- memset(&v3d->queue[i].stats, 0, sizeof(v3d->queue[i].stats));
+ struct v3d_queue_state *queue = &v3d->queue[i];
+
+ queue->fence_context = dma_fence_context_alloc(1);
+ memset(&queue->stats, 0, sizeof(queue->stats));
+ rwlock_init(&queue->stats.rw_lock);
}
spin_lock_init(&v3d->mm_lock);
diff --git a/drivers/gpu/drm/v3d/v3d_sched.c b/drivers/gpu/drm/v3d/v3d_sched.c
index 754107b80f67..640de6768b15 100644
--- a/drivers/gpu/drm/v3d/v3d_sched.c
+++ b/drivers/gpu/drm/v3d/v3d_sched.c
@@ -113,19 +113,28 @@ v3d_job_start_stats(struct v3d_job *job, enum v3d_queue queue)
struct v3d_stats *global_stats = &v3d->queue[queue].stats;
struct v3d_stats *local_stats = &file->stats[queue];
u64 now = local_clock();
+ unsigned long flags;
+ write_lock_irqsave(&local_stats->rw_lock, flags);
local_stats->start_ns = now;
+ write_unlock_irqrestore(&local_stats->rw_lock, flags);
+
+ write_lock_irqsave(&global_stats->rw_lock, flags);
global_stats->start_ns = now;
+ write_unlock_irqrestore(&global_stats->rw_lock, flags);
}
static void
v3d_stats_update(struct v3d_stats *stats)
{
u64 now = local_clock();
+ unsigned long flags;
+ write_lock_irqsave(&stats->rw_lock, flags);
stats->enabled_ns += now - stats->start_ns;
stats->jobs_sent++;
stats->start_ns = 0;
+ write_unlock_irqrestore(&stats->rw_lock, flags);
}
void
diff --git a/drivers/gpu/drm/v3d/v3d_sysfs.c b/drivers/gpu/drm/v3d/v3d_sysfs.c
index 1eb5f3de6937..0f739a034cee 100644
--- a/drivers/gpu/drm/v3d/v3d_sysfs.c
+++ b/drivers/gpu/drm/v3d/v3d_sysfs.c
@@ -15,18 +15,20 @@ gpu_stats_show(struct device *dev, struct device_attribute *attr, char *buf)
struct v3d_dev *v3d = to_v3d_dev(drm);
enum v3d_queue queue;
u64 timestamp = local_clock();
- u64 active_runtime;
ssize_t len = 0;
+ unsigned long flags;
len += sysfs_emit(buf, "queue\ttimestamp\tjobs\truntime\n");
for (queue = 0; queue < V3D_MAX_QUEUES; queue++) {
struct v3d_stats *stats = &v3d->queue[queue].stats;
+ u64 active_runtime, jobs_sent;
- if (stats->start_ns)
- active_runtime = timestamp - stats->start_ns;
- else
- active_runtime = 0;
+ read_lock_irqsave(&stats->rw_lock, flags);
+ active_runtime = stats->start_ns ? stats->enabled_ns + timestamp - stats->start_ns
+ : stats->enabled_ns;
+ jobs_sent = stats->jobs_sent;
+ read_unlock_irqrestore(&stats->rw_lock, flags);
/* Each line will display the queue name, timestamp, the number
* of jobs sent to that queue and the runtime, as can be seem here:
@@ -40,9 +42,7 @@ gpu_stats_show(struct device *dev, struct device_attribute *attr, char *buf)
*/
len += sysfs_emit_at(buf, len, "%s\t%llu\t%llu\t%llu\n",
v3d_queue_to_string(queue),
- timestamp,
- stats->jobs_sent,
- stats->enabled_ns + active_runtime);
+ timestamp, jobs_sent, active_runtime);
}
return len;
--
2.44.0
