Re: [Intel-gfx] [PATCH v3 4/7] drm/i915: Switch to fdinfo helper

[Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>]

On 11/04/2023 23:56, Rob Clark wrote:
> From: Rob Clark <robdclark@chromium.org>
> 
> Signed-off-by: Rob Clark <robdclark@chromium.org>
> ---
>   drivers/gpu/drm/i915/i915_driver.c     |  3 ++-
>   drivers/gpu/drm/i915/i915_drm_client.c | 18 +++++-------------
>   drivers/gpu/drm/i915/i915_drm_client.h |  2 +-
>   3 files changed, 8 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/gpu/drm/i915/i915_driver.c b/drivers/gpu/drm/i915/i915_driver.c
> index db7a86def7e2..37eacaa3064b 100644
> --- a/drivers/gpu/drm/i915/i915_driver.c
> +++ b/drivers/gpu/drm/i915/i915_driver.c
> @@ -1696,7 +1696,7 @@ static const struct file_operations i915_driver_fops = {
>   	.compat_ioctl = i915_ioc32_compat_ioctl,
>   	.llseek = noop_llseek,
>   #ifdef CONFIG_PROC_FS
> -	.show_fdinfo = i915_drm_client_fdinfo,
> +	.show_fdinfo = drm_fop_show_fdinfo,
>   #endif
>   };
>   
> @@ -1796,6 +1796,7 @@ static const struct drm_driver i915_drm_driver = {
>   	.open = i915_driver_open,
>   	.lastclose = i915_driver_lastclose,
>   	.postclose = i915_driver_postclose,
> +	.show_fdinfo = i915_drm_client_fdinfo,
>   
>   	.prime_handle_to_fd = drm_gem_prime_handle_to_fd,
>   	.prime_fd_to_handle = drm_gem_prime_fd_to_handle,
> diff --git a/drivers/gpu/drm/i915/i915_drm_client.c b/drivers/gpu/drm/i915/i915_drm_client.c
> index b09d1d386574..4a77e5e47f79 100644
> --- a/drivers/gpu/drm/i915/i915_drm_client.c
> +++ b/drivers/gpu/drm/i915/i915_drm_client.c
> @@ -101,7 +101,7 @@ static u64 busy_add(struct i915_gem_context *ctx, unsigned int class)
>   }
>   
>   static void
> -show_client_class(struct seq_file *m,
> +show_client_class(struct drm_printer *p,
>   		  struct i915_drm_client *client,
>   		  unsigned int class)
>   {
> @@ -117,22 +117,20 @@ show_client_class(struct seq_file *m,
>   	rcu_read_unlock();
>   
>   	if (capacity)
> -		seq_printf(m, "drm-engine-%s:\t%llu ns\n",
> +		drm_printf(p, "drm-engine-%s:\t%llu ns\n",
>   			   uabi_class_names[class], total);
>   
>   	if (capacity > 1)
> -		seq_printf(m, "drm-engine-capacity-%s:\t%u\n",
> +		drm_printf(p, "drm-engine-capacity-%s:\t%u\n",
>   			   uabi_class_names[class],
>   			   capacity);
>   }
>   
> -void i915_drm_client_fdinfo(struct seq_file *m, struct file *f)
> +void i915_drm_client_fdinfo(struct drm_printer *p, struct drm_file *file)
>   {
> -	struct drm_file *file = f->private_data;
>   	struct drm_i915_file_private *file_priv = file->driver_priv;
>   	struct drm_i915_private *i915 = file_priv->dev_priv;
>   	struct i915_drm_client *client = file_priv->client;
> -	struct pci_dev *pdev = to_pci_dev(i915->drm.dev);
>   	unsigned int i;
>   
>   	/*
> @@ -141,12 +139,6 @@ void i915_drm_client_fdinfo(struct seq_file *m, struct file *f)
>   	 * ******************************************************************
>   	 */
>   
> -	seq_printf(m, "drm-driver:\t%s\n", i915->drm.driver->name);
> -	seq_printf(m, "drm-pdev:\t%04x:%02x:%02x.%d\n",
> -		   pci_domain_nr(pdev->bus), pdev->bus->number,
> -		   PCI_SLOT(pdev->devfn), PCI_FUNC(pdev->devfn));
> -	seq_printf(m, "drm-client-id:\t%u\n", client->id);

As mentioned in my reply to the cover letter, I think the i915 
implementation is the right one. At least the semantics of it.

Granted it is a super set of the minimum required as documented by 
drm-usage-stats.rst - not only 1:1 to current instances of struct file, 
but also avoids immediate id recycling.

Former could perhaps be achieved with a simple pointer hash, but latter 
helps userspace detect when a client has exited and id re-allocated to a 
new client within a single scanning period.

Without this I don't think userspace can implement a fail safe method of 
detecting which clients are new ones and so wouldn't be able to track 
history correctly.

I think we should rather extend the documented contract to include the 
cyclical property than settle for a weaker common implementation.

Regards,

Tvrtko

> -
>   	/*
>   	 * Temporarily skip showing client engine information with GuC submission till
>   	 * fetching engine busyness is implemented in the GuC submission backend
> @@ -155,6 +147,6 @@ void i915_drm_client_fdinfo(struct seq_file *m, struct file *f)
>   		return;
>   
>   	for (i = 0; i < ARRAY_SIZE(uabi_class_names); i++)
> -		show_client_class(m, client, i);
> +		show_client_class(p, client, i);
>   }
>   #endif
> diff --git a/drivers/gpu/drm/i915/i915_drm_client.h b/drivers/gpu/drm/i915/i915_drm_client.h
> index 69496af996d9..ef85fef45de5 100644
> --- a/drivers/gpu/drm/i915/i915_drm_client.h
> +++ b/drivers/gpu/drm/i915/i915_drm_client.h
> @@ -60,7 +60,7 @@ static inline void i915_drm_client_put(struct i915_drm_client *client)
>   struct i915_drm_client *i915_drm_client_add(struct i915_drm_clients *clients);
>   
>   #ifdef CONFIG_PROC_FS
> -void i915_drm_client_fdinfo(struct seq_file *m, struct file *f);
> +void i915_drm_client_fdinfo(struct drm_printer *p, struct drm_file *file);
>   #endif
>   
>   void i915_drm_clients_fini(struct i915_drm_clients *clients);