[Intel-gfx] [RFC 3/3] drm/i915: Export engine busy stats in debugfs

[Dmitry Rogozhkin]

On 5/9/2017 7:09 AM, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
>
> Export the stats added in the previous patch in debugfs.
>
> Number of active clients reading this data is tracked and the
> static key is only enabled whilst there are some.
>
> Userspace is intended to keep the file descriptor open, seeking
> to the beginning of the file periodically, and re-reading the
> stats.
>
> This is because the underlying implementation is costly on every
> first open/last close transition, and also, because the stats
> exported mostly make sense when they are considered relative to
> the previous sample.
>
> File lists nanoseconds each engine was active since the tracking
> has started.
>
> Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> ---
>   drivers/gpu/drm/i915/i915_debugfs.c | 120 ++++++++++++++++++++++++++++++++++++
>   1 file changed, 120 insertions(+)
>
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index 1003511f28cc..db588ef858cb 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -4752,6 +4752,120 @@ static const struct file_operations i915_hpd_storm_ctl_fops = {
>   	.write = i915_hpd_storm_ctl_write
>   };
>   
> +DECLARE_STATIC_KEY_FALSE(i915_engine_stats_key);
> +static DEFINE_MUTEX(i915_engine_stats_mutex);
> +static int i915_engine_stats_ref;
> +
> +struct i915_engine_stats_buf {
> +	unsigned int len;
> +	size_t available;
> +	char buf[0];
> +};
> +
> +static int i915_engine_stats_open(struct inode *inode, struct file *file)
> +{
> +	const unsigned int engine_name_len =
> +		sizeof(((struct intel_engine_cs *)0)->name);
> +	struct i915_engine_stats_buf *buf;
> +	const unsigned int buf_size =
> +		(engine_name_len + 2 + 19 + 1) * I915_NUM_ENGINES + 1 +
> +		sizeof(*buf);
> +	int ret;
> +
> +	buf = kzalloc(buf_size, GFP_KERNEL);
> +	if (!buf)
> +		return -ENOMEM;
> +
> +	buf->len = buf_size;
> +	file->private_data = buf;
> +
> +	ret = mutex_lock_interruptible(&i915_engine_stats_mutex);
> +	if (ret)
> +		return ret;
> +
> +	if (i915_engine_stats_ref++ == 0) {
> +		struct drm_i915_private *dev_priv = file->f_inode->i_private;
> +		struct intel_engine_cs *engine;
> +		enum intel_engine_id id;
> +
> +		for_each_engine(engine, dev_priv, id) {
> +			memset(&engine->stats, 0, sizeof(engine->stats));
> +			spin_lock_init(&engine->stats.lock);
> +		}
> +
> +		static_branch_enable(&i915_engine_stats_key);
> +	}
> +
> +	mutex_unlock(&i915_engine_stats_mutex);
> +
> +	return 0;
> +}
> +
> +static int i915_engine_stats_release(struct inode *inode, struct file *file)
> +{
> +	mutex_lock(&i915_engine_stats_mutex);
> +	if (--i915_engine_stats_ref == 0)
> +		static_branch_disable(&i915_engine_stats_key);
> +	mutex_unlock(&i915_engine_stats_mutex);
> +
> +	kfree(file->private_data);
> +
> +	return 0;
> +}
> +
> +static ssize_t i915_engine_stats_read(struct file *file, char __user *ubuf,
> +				      size_t count, loff_t *pos)
> +{
> +	struct i915_engine_stats_buf *buf =
> +		(struct i915_engine_stats_buf *)file->private_data;
> +
> +	if (*pos == 0) {
> +		struct drm_i915_private *dev_priv = file->f_inode->i_private;
> +		char *ptr = &buf->buf[0];
> +		int left = buf->len;
> +		struct intel_engine_cs *engine;
> +		enum intel_engine_id id;
> +
> +		buf->available = 0;
> +
> +		for_each_engine(engine, dev_priv, id) {
> +			u64 total;
> +			int len;
> +
> +			spin_lock_irq(&engine->stats.lock);
> +			total = engine->stats.total;
> +			/*
> +			 * If the engine is executing something at the moment
> +			 * add it to the total.
> +			 */
> +			if (engine->stats.ref)
> +				total += ktime_get_real_ns() -
> +					 engine->stats.start;
> +			spin_unlock_irq(&engine->stats.lock);
> +
> +			len = snprintf(ptr, left, "%s: %llu\n",
> +				       engine->name, total);
If I caught it right, file format is:
   render ring: 12345
   bsd ring: 12345
   ...
where numbers are busy clocks (ns) from the system boot time. Is that 
right? What if we will want to expose some other statistics information 
later, not only busy clocks? For example, engines i915 queues depths is 
a next interest. Maybe later we will find something else interesting. 
So, do we want to consider this file to contain all kind of statistics 
in the future, and hence it should be of somewhat different format, or 
it will have only busy clocks, and maybe we need other file name then?
> +			buf->available += len;
> +			left -= len;
> +			ptr += len;
> +
> +			if (len == 0)
> +				return -EFBIG;
> +		}
> +	}
> +
> +	return simple_read_from_buffer(ubuf, count, pos, &buf->buf[0],
> +				       buf->available);
> +}
> +
> +static const struct file_operations i915_engine_stats_fops = {
> +	.owner = THIS_MODULE,
> +	.open = i915_engine_stats_open,
> +	.release = i915_engine_stats_release,
> +	.read = i915_engine_stats_read,
> +	.llseek = default_llseek,
> +};
> +
>   static const struct drm_info_list i915_debugfs_list[] = {
>   	{"i915_capabilities", i915_capabilities, 0},
>   	{"i915_gem_objects", i915_gem_object_info, 0},
> @@ -4839,6 +4953,12 @@ int i915_debugfs_register(struct drm_i915_private *dev_priv)
>   	struct dentry *ent;
>   	int ret, i;
>   
> +	ent = debugfs_create_file("i915_engine_stats", S_IRUGO,
> +				  minor->debugfs_root, to_i915(minor->dev),
> +				  &i915_engine_stats_fops);
> +	if (!ent)
> +		return -ENOMEM;
> +
>   	ent = debugfs_create_file("i915_forcewake_user", S_IRUSR,
>   				  minor->debugfs_root, to_i915(minor->dev),
>   				  &i915_forcewake_fops);