[Intel-gfx] [PATCH 11/15] drm/i915: Trim i915_guc_info() stack usage

[Tvrtko Ursulin]

On 25/11/2016 09:30, Chris Wilson wrote:
> i915_guc_info() (part of debugfs output) tries to avoid holding
> struct_mutex for a long period by copying onto the stack. This causes a
> warning that the stack frame is massive, so stop doing that. We can even
> forgo holding the struct_mutex here as that doesn't serialise the values
> being read (and the lists used exist for the device lifetime).
>
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>
> ---
>  drivers/gpu/drm/i915/i915_debugfs.c | 39 +++++++++++++------------------------
>  1 file changed, 14 insertions(+), 25 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_debugfs.c b/drivers/gpu/drm/i915/i915_debugfs.c
> index 8eb8c29b7492..7676e88ae5f2 100644
> --- a/drivers/gpu/drm/i915/i915_debugfs.c
> +++ b/drivers/gpu/drm/i915/i915_debugfs.c
> @@ -2434,47 +2434,36 @@ static void i915_guc_client_info(struct seq_file *m,
>  static int i915_guc_info(struct seq_file *m, void *data)
>  {
>  	struct drm_i915_private *dev_priv = node_to_i915(m->private);
> -	struct drm_device *dev = &dev_priv->drm;
> -	struct intel_guc guc;
> -	struct i915_guc_client client = {};
> +	const struct intel_guc *guc = &dev_priv->guc;
>  	struct intel_engine_cs *engine;
>  	enum intel_engine_id id;
> -	u64 total = 0;
> +	u64 total;
>
>  	if (!HAS_GUC_SCHED(dev_priv))
>  		return 0;
>
> -	if (mutex_lock_interruptible(&dev->struct_mutex))
> -		return 0;
> -
> -	/* Take a local copy of the GuC data, so we can dump it at leisure */
> -	guc = dev_priv->guc;
> -	if (guc.execbuf_client)
> -		client = *guc.execbuf_client;

So this used to print out all zeros when GuC submission is disabled. 
Should we instead just skip all the counter dumping if execbuf_client == 
NULL and just print "disabled" or something?

> -
> -	mutex_unlock(&dev->struct_mutex);
> -
>  	seq_printf(m, "Doorbell map:\n");
> -	seq_printf(m, "\t%*pb\n", GUC_MAX_DOORBELLS, guc.doorbell_bitmap);
> -	seq_printf(m, "Doorbell next cacheline: 0x%x\n\n", guc.db_cacheline);
> +	seq_printf(m, "\t%*pb\n", GUC_MAX_DOORBELLS, guc->doorbell_bitmap);
> +	seq_printf(m, "Doorbell next cacheline: 0x%x\n\n", guc->db_cacheline);
>
> -	seq_printf(m, "GuC total action count: %llu\n", guc.action_count);
> -	seq_printf(m, "GuC action failure count: %u\n", guc.action_fail);
> -	seq_printf(m, "GuC last action command: 0x%x\n", guc.action_cmd);
> -	seq_printf(m, "GuC last action status: 0x%x\n", guc.action_status);
> -	seq_printf(m, "GuC last action error code: %d\n", guc.action_err);
> +	seq_printf(m, "GuC total action count: %llu\n", guc->action_count);
> +	seq_printf(m, "GuC action failure count: %u\n", guc->action_fail);
> +	seq_printf(m, "GuC last action command: 0x%x\n", guc->action_cmd);
> +	seq_printf(m, "GuC last action status: 0x%x\n", guc->action_status);
> +	seq_printf(m, "GuC last action error code: %d\n", guc->action_err);
>
> +	total = 0;
>  	seq_printf(m, "\nGuC submissions:\n");
>  	for_each_engine(engine, dev_priv, id) {
> -		u64 submissions = guc.submissions[id];
> +		u64 submissions = guc->submissions[id];
>  		total += submissions;
>  		seq_printf(m, "\t%-24s: %10llu, last seqno 0x%08x\n",
> -			engine->name, submissions, guc.last_seqno[id]);
> +			engine->name, submissions, guc->last_seqno[id]);
>  	}
>  	seq_printf(m, "\t%s: %llu\n", "Total", total);
>
> -	seq_printf(m, "\nGuC execbuf client @ %p:\n", guc.execbuf_client);
> -	i915_guc_client_info(m, dev_priv, &client);
> +	seq_printf(m, "\nGuC execbuf client @ %p:\n", guc->execbuf_client);

Dereferencing guc->execbuf_client doesn't oops in execlist mode? I must 
be misreading something in that case.

> +	i915_guc_client_info(m, dev_priv, guc->execbuf_client);
>
>  	i915_guc_log_info(m, dev_priv);
>
>

Regards,

Tvrtko