Re: [RFC 4/5] drm/i915: Expose per-engine client busyness

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On 14/02/2018 19:17, Chris Wilson wrote:
Quoting Tvrtko Ursulin (2018-02-14 18:50:34)
From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>

Expose per-client and per-engine busyness under the previously added sysfs
client root.

The new files are one per-engine instance and located under the 'busy'
directory.

Each contains a monotonically increasing nano-second resolution times each
client's jobs were executing on the GPU.

$ cat /sys/class/drm/card0/clients/5/busy/rcs0
32516602

This data can serve as an interface to implement a top like utility for
GPU jobs. For instance I have prototyped a tool in IGT which produces
periodic output like:

neverball[  6011]:  rcs0:  41.01%  bcs0:   0.00%  vcs0:   0.00%  vecs0:   0.00%
      Xorg[  5664]:  rcs0:  31.16%  bcs0:   0.00%  vcs0:   0.00%  vecs0:   0.00%
     xfwm4[  5727]:  rcs0:   0.00%  bcs0:   0.00%  vcs0:   0.00%  vecs0:   0.00%

This tools can also be extended to use the i915 PMU and show overall engine
busyness, and engine loads using the queue depth metric.

v2: Use intel_context_engine_get_busy_time.
v3: New directory structure.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
---
  drivers/gpu/drm/i915/i915_drv.h |  8 ++++
  drivers/gpu/drm/i915/i915_gem.c | 86 +++++++++++++++++++++++++++++++++++++++--
  2 files changed, 91 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/i915/i915_drv.h b/drivers/gpu/drm/i915/i915_drv.h
index 372d13cb2472..d6b2883b42fe 100644
--- a/drivers/gpu/drm/i915/i915_drv.h
+++ b/drivers/gpu/drm/i915/i915_drv.h
@@ -315,6 +315,12 @@ struct drm_i915_private;
  struct i915_mm_struct;
  struct i915_mmu_object;
+struct i915_engine_busy_attribute {
+       struct device_attribute attr;
+       struct drm_i915_file_private *file_priv;
+       struct intel_engine_cs *engine;
+};
+
  struct drm_i915_file_private {
         struct drm_i915_private *dev_priv;
         struct drm_file *file;
@@ -350,10 +356,12 @@ struct drm_i915_file_private {
         unsigned int client_pid;
         char *client_name;
         struct kobject *client_root;
+       struct kobject *busy_root;
struct {
                 struct device_attribute pid;
                 struct device_attribute name;
+               struct i915_engine_busy_attribute busy[I915_NUM_ENGINES];
         } attr;
  };
diff --git a/drivers/gpu/drm/i915/i915_gem.c b/drivers/gpu/drm/i915/i915_gem.c
index 46ac7b3ca348..01298d924524 100644
--- a/drivers/gpu/drm/i915/i915_gem.c
+++ b/drivers/gpu/drm/i915/i915_gem.c
@@ -5631,6 +5631,45 @@ show_client_pid(struct device *kdev, struct device_attribute *attr, char *buf)
         return snprintf(buf, PAGE_SIZE, "%u", file_priv->client_pid);
  }
+struct busy_ctx {
+       struct intel_engine_cs *engine;
+       u64 total;
+};
+
+static int busy_add(int _id, void *p, void *data)
+{
+       struct i915_gem_context *ctx = p;
+       struct busy_ctx *bc = data;
+
+       bc->total +=
+               ktime_to_ns(intel_context_engine_get_busy_time(ctx,
+                                                              bc->engine));
+
+       return 0;
+}
+
+static ssize_t
+show_client_busy(struct device *kdev, struct device_attribute *attr, char *buf)
+{
+       struct i915_engine_busy_attribute *i915_attr =
+               container_of(attr, typeof(*i915_attr), attr);
+       struct drm_i915_file_private *file_priv = i915_attr->file_priv;
+       struct intel_engine_cs *engine = i915_attr->engine;
+       struct drm_i915_private *i915 = engine->i915;
+       struct busy_ctx bc = { .engine = engine };
+       int ret;
+
+       ret = i915_mutex_lock_interruptible(&i915->drm);
+       if (ret)
+               return ret;
+

Doesn't need struct_mutex, just rcu_read_lock() will suffice.

Neither the context nor idr will be freed too soon, and the data is
involatile when the context is unreffed (and contexts don't have the
nasty zombie/undead status of requests). So the busy-time will be
stable.

Are you sure? What holds a reference to contexts while userspace might by in sysfs reading the stat? It would be super nice if we could avoid struct mutex here.. I just don't understand at the moment why it would be safe.

Regards,

Tvrtko
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