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

Tvrtko Ursulin
2023-04-12T12:32:58Z

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);