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Date: Wed, 1 May 2024 18:30:53 +0200
From: Daniel Vetter <daniel@ffwll.ch>
To: =?iso-8859-1?Q?Adri=E1n?= Larumbe <adrian.larumbe@collabora.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	Maxime Ripard <mripard@kernel.org>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	David Airlie <airlied@gmail.com>, Daniel Vetter <daniel@ffwll.ch>,
	Hans de Goede <hdegoede@redhat.com>, kernel@collabora.com,
	Boris Brezillon <boris.brezillon@collabora.com>,
	Tvrtko Ursulin <tursulin@ursulin.net>,
	Christopher Healy <healych@amazon.com>,
	dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] drm/sysfs: Add drm class-wide attribute to get active
 device clients
Message-ID: <ZjJuPQBNnu41Djrr@phenom.ffwll.local>
Mail-Followup-To: =?iso-8859-1?Q?Adri=E1n?= Larumbe <adrian.larumbe@collabora.com>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	Maxime Ripard <mripard@kernel.org>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	David Airlie <airlied@gmail.com>,
	Hans de Goede <hdegoede@redhat.com>, kernel@collabora.com,
	Boris Brezillon <boris.brezillon@collabora.com>,
	Tvrtko Ursulin <tursulin@ursulin.net>,
	Christopher Healy <healych@amazon.com>,
	dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
References: <20240403182951.724488-1-adrian.larumbe@collabora.com>
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In-Reply-To: <20240403182951.724488-1-adrian.larumbe@collabora.com>

On Wed, Apr 03, 2024 at 07:29:39PM +0100, Adri?n Larumbe wrote:
> Up to this day, all fdinfo-based GPU profilers must traverse the entire
> /proc directory structure to find open DRM clients with fdinfo file
> descriptors. This is inefficient and time-consuming.
> 
> This patch adds a new device class attribute that will install a sysfs file
> per DRM device, which can be queried by profilers to get a list of PIDs for
> their open clients. This file isn't human-readable, and it's meant to be
> queried only by GPU profilers like gputop and nvtop.
> 
> Cc: Boris Brezillon <boris.brezillon@collabora.com>
> Cc: Tvrtko Ursulin <tursulin@ursulin.net>
> Cc: Christopher Healy <healych@amazon.com>
> Signed-off-by: Adri?n Larumbe <adrian.larumbe@collabora.com>

Tvrtko pointed me at this on irc and .. uh I think this definitely needs
an ack from Greg KH before we can land it. It's quite far away from what
sysfs uapi usually looks like and also semantically does ...
-Sima

> ---
>  drivers/gpu/drm/drm_internal.h       |  2 +-
>  drivers/gpu/drm/drm_privacy_screen.c |  2 +-
>  drivers/gpu/drm/drm_sysfs.c          | 89 ++++++++++++++++++++++------
>  3 files changed, 74 insertions(+), 19 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_internal.h b/drivers/gpu/drm/drm_internal.h
> index 2215baef9a3e..9a399b03d11c 100644
> --- a/drivers/gpu/drm/drm_internal.h
> +++ b/drivers/gpu/drm/drm_internal.h
> @@ -145,7 +145,7 @@ bool drm_master_internal_acquire(struct drm_device *dev);
>  void drm_master_internal_release(struct drm_device *dev);
>  
>  /* drm_sysfs.c */
> -extern struct class *drm_class;
> +extern struct class drm_class;
>  
>  int drm_sysfs_init(void);
>  void drm_sysfs_destroy(void);
> diff --git a/drivers/gpu/drm/drm_privacy_screen.c b/drivers/gpu/drm/drm_privacy_screen.c
> index 6cc39e30781f..2fbd24ba5818 100644
> --- a/drivers/gpu/drm/drm_privacy_screen.c
> +++ b/drivers/gpu/drm/drm_privacy_screen.c
> @@ -401,7 +401,7 @@ struct drm_privacy_screen *drm_privacy_screen_register(
>  	mutex_init(&priv->lock);
>  	BLOCKING_INIT_NOTIFIER_HEAD(&priv->notifier_head);
>  
> -	priv->dev.class = drm_class;
> +	priv->dev.class = &drm_class;
>  	priv->dev.type = &drm_privacy_screen_type;
>  	priv->dev.parent = parent;
>  	priv->dev.release = drm_privacy_screen_device_release;
> diff --git a/drivers/gpu/drm/drm_sysfs.c b/drivers/gpu/drm/drm_sysfs.c
> index a953f69a34b6..56ca9e22c720 100644
> --- a/drivers/gpu/drm/drm_sysfs.c
> +++ b/drivers/gpu/drm/drm_sysfs.c
> @@ -58,8 +58,6 @@ static struct device_type drm_sysfs_device_connector = {
>  	.name = "drm_connector",
>  };
>  
> -struct class *drm_class;
> -
>  #ifdef CONFIG_ACPI
>  static bool drm_connector_acpi_bus_match(struct device *dev)
>  {
> @@ -128,6 +126,62 @@ static const struct component_ops typec_connector_ops = {
>  
>  static CLASS_ATTR_STRING(version, S_IRUGO, "drm 1.1.0 20060810");
>  
> +static ssize_t clients_show(struct device *cd, struct device_attribute *attr, char *buf)
> +{
> +	struct drm_minor *minor = cd->driver_data;
> +	struct drm_device *ddev = minor->dev;
> +	struct drm_file *priv;
> +	ssize_t offset = 0;
> +	void *pid_buf;
> +
> +	if (minor->type != DRM_MINOR_RENDER)
> +		return 0;
> +
> +	pid_buf = kvmalloc(PAGE_SIZE, GFP_KERNEL);
> +	if (!pid_buf)
> +		return 0;
> +
> +	mutex_lock(&ddev->filelist_mutex);
> +	list_for_each_entry_reverse(priv, &ddev->filelist, lhead) {
> +		struct pid *pid;
> +
> +		if (drm_WARN_ON(ddev, (PAGE_SIZE - offset) < sizeof(pid_t)))
> +			break;
> +
> +		rcu_read_lock();
> +		pid = rcu_dereference(priv->pid);
> +		(*(pid_t *)(pid_buf + offset)) = pid_vnr(pid);
> +		rcu_read_unlock();
> +
> +		offset += sizeof(pid_t);
> +	}
> +	mutex_unlock(&ddev->filelist_mutex);
> +
> +	if (offset < PAGE_SIZE)
> +		(*(pid_t *)(pid_buf + offset)) = 0;
> +
> +	memcpy(buf, pid_buf, offset);
> +
> +	kvfree(pid_buf);
> +
> +	return offset;
> +
> +}
> +static DEVICE_ATTR_RO(clients);
> +
> +static struct attribute *drm_device_attrs[] = {
> +	&dev_attr_clients.attr,
> +	NULL,
> +};
> +ATTRIBUTE_GROUPS(drm_device);
> +
> +struct class drm_class = {
> +	.name		= "drm",
> +	.dev_groups	= drm_device_groups,
> +};
> +
> +static bool drm_class_initialised;
> +
>  /**
>   * drm_sysfs_init - initialize sysfs helpers
>   *
> @@ -142,18 +196,19 @@ int drm_sysfs_init(void)
>  {
>  	int err;
>  
> -	drm_class = class_create("drm");
> -	if (IS_ERR(drm_class))
> -		return PTR_ERR(drm_class);
> +	err = class_register(&drm_class);
> +	if (err)
> +		return err;
>  
> -	err = class_create_file(drm_class, &class_attr_version.attr);
> +	err = class_create_file(&drm_class, &class_attr_version.attr);
>  	if (err) {
> -		class_destroy(drm_class);
> -		drm_class = NULL;
> +		class_destroy(&drm_class);
>  		return err;
>  	}
>  
> -	drm_class->devnode = drm_devnode;
> +	drm_class.devnode = drm_devnode;
> +
> +	drm_class_initialised = true;
>  
>  	drm_sysfs_acpi_register();
>  	return 0;
> @@ -166,12 +221,12 @@ int drm_sysfs_init(void)
>   */
>  void drm_sysfs_destroy(void)
>  {
> -	if (IS_ERR_OR_NULL(drm_class))
> +	if (!drm_class_initialised)
>  		return;
>  	drm_sysfs_acpi_unregister();
> -	class_remove_file(drm_class, &class_attr_version.attr);
> -	class_destroy(drm_class);
> -	drm_class = NULL;
> +	class_remove_file(&drm_class, &class_attr_version.attr);
> +	class_destroy(&drm_class);
> +	drm_class_initialised = false;
>  }
>  
>  static void drm_sysfs_release(struct device *dev)
> @@ -372,7 +427,7 @@ int drm_sysfs_connector_add(struct drm_connector *connector)
>  		return -ENOMEM;
>  
>  	device_initialize(kdev);
> -	kdev->class = drm_class;
> +	kdev->class = &drm_class;
>  	kdev->type = &drm_sysfs_device_connector;
>  	kdev->parent = dev->primary->kdev;
>  	kdev->groups = connector_dev_groups;
> @@ -550,7 +605,7 @@ struct device *drm_sysfs_minor_alloc(struct drm_minor *minor)
>  			minor_str = "card%d";
>  
>  		kdev->devt = MKDEV(DRM_MAJOR, minor->index);
> -		kdev->class = drm_class;
> +		kdev->class = &drm_class;
>  		kdev->type = &drm_sysfs_device_minor;
>  	}
>  
> @@ -579,10 +634,10 @@ struct device *drm_sysfs_minor_alloc(struct drm_minor *minor)
>   */
>  int drm_class_device_register(struct device *dev)
>  {
> -	if (!drm_class || IS_ERR(drm_class))
> +	if (!drm_class_initialised)
>  		return -ENOENT;
>  
> -	dev->class = drm_class;
> +	dev->class = &drm_class;
>  	return device_register(dev);
>  }
>  EXPORT_SYMBOL_GPL(drm_class_device_register);
> 
> base-commit: 45c734fdd43db14444025910b4c59dd2b8be714a
> -- 
> 2.44.0
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch