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

[Chris Wilson <chris@chris-wilson.co.uk>]

Quoting Tvrtko Ursulin (2018-02-14 18:50:34)
> From: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> 
> 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@intel.com>
> ---
>  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.
-Chris
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