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Subject: Re: [PATCH v2] dma-buf: Delete the DMA-BUF attachment sysfs
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To:     Hridya Valsaraju <hridya@google.com>,
        Sumit Semwal <sumit.semwal@linaro.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Daniel Vetter <daniel.vetter@ffwll.ch>,
        linux-kernel@vger.kernel.org, linux-media@vger.kernel.org,
        dri-devel@lists.freedesktop.org, linaro-mm-sig@lists.linaro.org
Cc:     kernel-team@android.com, john.stultz@linaro.org, surenb@google.com,
        daniel@ffwll.ch
References: <20210713040742.2680135-1-hridya@google.com>
From:   =?UTF-8?Q?Christian_K=c3=b6nig?= <christian.koenig@amd.com>
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Date:   Tue, 20 Jul 2021 11:11:43 +0200
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Am 13.07.21 um 06:07 schrieb Hridya Valsaraju:
> The DMA-BUF attachment statistics form a subset of the DMA-BUF
> sysfs statistics that recently merged to the drm-misc tree. They are not
> UABI yet since they have not merged to the upstream Linux kernel.
>
> Since there has been a reported a performance regression due to the
> overhead of sysfs directory creation/teardown during
> dma_buf_attach()/dma_buf_detach(), this patch deletes the DMA-BUF
> attachment statistics from sysfs.
>
> Fixes: bdb8d06dfefd (dmabuf: Add the capability to expose DMA-BUF stats
> in sysfs)
> Signed-off-by: Hridya Valsaraju <hridya@google.com>
> Reviewed-by: Christian König <christian.koenig@amd.com>
> Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
>
> Changes in v2:
> Updated commit message to clarify that the sysfs files being removed
> have not yet merged to upstream Linux and are hence not ABI.
>
> Hi Christian,
>
> I have updated the commit message as per your suggestion. Please do take
> another look when you get a chance.

I've just pushed that one to drm-misc-next. Sorry for the delay.

Regards,
Christian.

>
> Thanks,
> Hridya
>
>   .../ABI/testing/sysfs-kernel-dmabuf-buffers   |  28 ----
>   drivers/dma-buf/dma-buf-sysfs-stats.c         | 140 +-----------------
>   drivers/dma-buf/dma-buf-sysfs-stats.h         |  27 ----
>   drivers/dma-buf/dma-buf.c                     |  16 --
>   include/linux/dma-buf.h                       |  17 ---
>   5 files changed, 4 insertions(+), 224 deletions(-)
>
> diff --git a/Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers b/Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers
> index a243984ed420..5d3bc997dc64 100644
> --- a/Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers
> +++ b/Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers
> @@ -22,31 +22,3 @@ KernelVersion:	v5.13
>   Contact:	Hridya Valsaraju <hridya@google.com>
>   Description:	This file is read-only and specifies the size of the DMA-BUF in
>   		bytes.
> -
> -What:		/sys/kernel/dmabuf/buffers/<inode_number>/attachments
> -Date:		May 2021
> -KernelVersion:	v5.13
> -Contact:	Hridya Valsaraju <hridya@google.com>
> -Description:	This directory will contain subdirectories representing every
> -		attachment of the DMA-BUF.
> -
> -What:		/sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attachment_uid>
> -Date:		May 2021
> -KernelVersion:	v5.13
> -Contact:	Hridya Valsaraju <hridya@google.com>
> -Description:	This directory will contain information on the attached device
> -		and the number of current distinct device mappings.
> -
> -What:		/sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attachment_uid>/device
> -Date:		May 2021
> -KernelVersion:	v5.13
> -Contact:	Hridya Valsaraju <hridya@google.com>
> -Description:	This file is read-only and is a symlink to the attached device's
> -		sysfs entry.
> -
> -What:		/sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attachment_uid>/map_counter
> -Date:		May 2021
> -KernelVersion:	v5.13
> -Contact:	Hridya Valsaraju <hridya@google.com>
> -Description:	This file is read-only and contains a map_counter indicating the
> -		number of distinct device mappings of the attachment.
> diff --git a/drivers/dma-buf/dma-buf-sysfs-stats.c b/drivers/dma-buf/dma-buf-sysfs-stats.c
> index a2638e84199c..053baadcada9 100644
> --- a/drivers/dma-buf/dma-buf-sysfs-stats.c
> +++ b/drivers/dma-buf/dma-buf-sysfs-stats.c
> @@ -40,14 +40,11 @@
>    *
>    * * ``/sys/kernel/dmabuf/buffers/<inode_number>/exporter_name``
>    * * ``/sys/kernel/dmabuf/buffers/<inode_number>/size``
> - * * ``/sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attach_uid>/device``
> - * * ``/sys/kernel/dmabuf/buffers/<inode_number>/attachments/<attach_uid>/map_counter``
>    *
> - * The information in the interface can also be used to derive per-exporter and
> - * per-device usage statistics. The data from the interface can be gathered
> - * on error conditions or other important events to provide a snapshot of
> - * DMA-BUF usage. It can also be collected periodically by telemetry to monitor
> - * various metrics.
> + * The information in the interface can also be used to derive per-exporter
> + * statistics. The data from the interface can be gathered on error conditions
> + * or other important events to provide a snapshot of DMA-BUF usage.
> + * It can also be collected periodically by telemetry to monitor various metrics.
>    *
>    * Detailed documentation about the interface is present in
>    * Documentation/ABI/testing/sysfs-kernel-dmabuf-buffers.
> @@ -121,120 +118,6 @@ static struct kobj_type dma_buf_ktype = {
>   	.default_groups = dma_buf_stats_default_groups,
>   };
>   
> -#define to_dma_buf_attach_entry_from_kobj(x) container_of(x, struct dma_buf_attach_sysfs_entry, kobj)
> -
> -struct dma_buf_attach_stats_attribute {
> -	struct attribute attr;
> -	ssize_t (*show)(struct dma_buf_attach_sysfs_entry *sysfs_entry,
> -			struct dma_buf_attach_stats_attribute *attr, char *buf);
> -};
> -#define to_dma_buf_attach_stats_attr(x) container_of(x, struct dma_buf_attach_stats_attribute, attr)
> -
> -static ssize_t dma_buf_attach_stats_attribute_show(struct kobject *kobj,
> -						   struct attribute *attr,
> -						   char *buf)
> -{
> -	struct dma_buf_attach_stats_attribute *attribute;
> -	struct dma_buf_attach_sysfs_entry *sysfs_entry;
> -
> -	attribute = to_dma_buf_attach_stats_attr(attr);
> -	sysfs_entry = to_dma_buf_attach_entry_from_kobj(kobj);
> -
> -	if (!attribute->show)
> -		return -EIO;
> -
> -	return attribute->show(sysfs_entry, attribute, buf);
> -}
> -
> -static const struct sysfs_ops dma_buf_attach_stats_sysfs_ops = {
> -	.show = dma_buf_attach_stats_attribute_show,
> -};
> -
> -static ssize_t map_counter_show(struct dma_buf_attach_sysfs_entry *sysfs_entry,
> -				struct dma_buf_attach_stats_attribute *attr,
> -				char *buf)
> -{
> -	return sysfs_emit(buf, "%u\n", sysfs_entry->map_counter);
> -}
> -
> -static struct dma_buf_attach_stats_attribute map_counter_attribute =
> -	__ATTR_RO(map_counter);
> -
> -static struct attribute *dma_buf_attach_stats_default_attrs[] = {
> -	&map_counter_attribute.attr,
> -	NULL,
> -};
> -ATTRIBUTE_GROUPS(dma_buf_attach_stats_default);
> -
> -static void dma_buf_attach_sysfs_release(struct kobject *kobj)
> -{
> -	struct dma_buf_attach_sysfs_entry *sysfs_entry;
> -
> -	sysfs_entry = to_dma_buf_attach_entry_from_kobj(kobj);
> -	kfree(sysfs_entry);
> -}
> -
> -static struct kobj_type dma_buf_attach_ktype = {
> -	.sysfs_ops = &dma_buf_attach_stats_sysfs_ops,
> -	.release = dma_buf_attach_sysfs_release,
> -	.default_groups = dma_buf_attach_stats_default_groups,
> -};
> -
> -void dma_buf_attach_stats_teardown(struct dma_buf_attachment *attach)
> -{
> -	struct dma_buf_attach_sysfs_entry *sysfs_entry;
> -
> -	sysfs_entry = attach->sysfs_entry;
> -	if (!sysfs_entry)
> -		return;
> -
> -	sysfs_delete_link(&sysfs_entry->kobj, &attach->dev->kobj, "device");
> -
> -	kobject_del(&sysfs_entry->kobj);
> -	kobject_put(&sysfs_entry->kobj);
> -}
> -
> -int dma_buf_attach_stats_setup(struct dma_buf_attachment *attach,
> -			       unsigned int uid)
> -{
> -	struct dma_buf_attach_sysfs_entry *sysfs_entry;
> -	int ret;
> -	struct dma_buf *dmabuf;
> -
> -	if (!attach)
> -		return -EINVAL;
> -
> -	dmabuf = attach->dmabuf;
> -
> -	sysfs_entry = kzalloc(sizeof(struct dma_buf_attach_sysfs_entry),
> -			      GFP_KERNEL);
> -	if (!sysfs_entry)
> -		return -ENOMEM;
> -
> -	sysfs_entry->kobj.kset = dmabuf->sysfs_entry->attach_stats_kset;
> -
> -	attach->sysfs_entry = sysfs_entry;
> -
> -	ret = kobject_init_and_add(&sysfs_entry->kobj, &dma_buf_attach_ktype,
> -				   NULL, "%u", uid);
> -	if (ret)
> -		goto kobj_err;
> -
> -	ret = sysfs_create_link(&sysfs_entry->kobj, &attach->dev->kobj,
> -				"device");
> -	if (ret)
> -		goto link_err;
> -
> -	return 0;
> -
> -link_err:
> -	kobject_del(&sysfs_entry->kobj);
> -kobj_err:
> -	kobject_put(&sysfs_entry->kobj);
> -	attach->sysfs_entry = NULL;
> -
> -	return ret;
> -}
>   void dma_buf_stats_teardown(struct dma_buf *dmabuf)
>   {
>   	struct dma_buf_sysfs_entry *sysfs_entry;
> @@ -243,7 +126,6 @@ void dma_buf_stats_teardown(struct dma_buf *dmabuf)
>   	if (!sysfs_entry)
>   		return;
>   
> -	kset_unregister(sysfs_entry->attach_stats_kset);
>   	kobject_del(&sysfs_entry->kobj);
>   	kobject_put(&sysfs_entry->kobj);
>   }
> @@ -290,7 +172,6 @@ int dma_buf_stats_setup(struct dma_buf *dmabuf)
>   {
>   	struct dma_buf_sysfs_entry *sysfs_entry;
>   	int ret;
> -	struct kset *attach_stats_kset;
>   
>   	if (!dmabuf || !dmabuf->file)
>   		return -EINVAL;
> @@ -315,21 +196,8 @@ int dma_buf_stats_setup(struct dma_buf *dmabuf)
>   	if (ret)
>   		goto err_sysfs_dmabuf;
>   
> -	/* create the directory for attachment stats */
> -	attach_stats_kset = kset_create_and_add("attachments",
> -						&dmabuf_sysfs_no_uevent_ops,
> -						&sysfs_entry->kobj);
> -	if (!attach_stats_kset) {
> -		ret = -ENOMEM;
> -		goto err_sysfs_attach;
> -	}
> -
> -	sysfs_entry->attach_stats_kset = attach_stats_kset;
> -
>   	return 0;
>   
> -err_sysfs_attach:
> -	kobject_del(&sysfs_entry->kobj);
>   err_sysfs_dmabuf:
>   	kobject_put(&sysfs_entry->kobj);
>   	dmabuf->sysfs_entry = NULL;
> diff --git a/drivers/dma-buf/dma-buf-sysfs-stats.h b/drivers/dma-buf/dma-buf-sysfs-stats.h
> index 5f4703249117..a49c6e2650cc 100644
> --- a/drivers/dma-buf/dma-buf-sysfs-stats.h
> +++ b/drivers/dma-buf/dma-buf-sysfs-stats.h
> @@ -14,23 +14,8 @@ int dma_buf_init_sysfs_statistics(void);
>   void dma_buf_uninit_sysfs_statistics(void);
>   
>   int dma_buf_stats_setup(struct dma_buf *dmabuf);
> -int dma_buf_attach_stats_setup(struct dma_buf_attachment *attach,
> -			       unsigned int uid);
> -static inline void dma_buf_update_attachment_map_count(struct dma_buf_attachment *attach,
> -						       int delta)
> -{
> -	struct dma_buf_attach_sysfs_entry *entry = attach->sysfs_entry;
>   
> -	entry->map_counter += delta;
> -}
>   void dma_buf_stats_teardown(struct dma_buf *dmabuf);
> -void dma_buf_attach_stats_teardown(struct dma_buf_attachment *attach);
> -static inline unsigned int dma_buf_update_attach_uid(struct dma_buf *dmabuf)
> -{
> -	struct dma_buf_sysfs_entry *entry = dmabuf->sysfs_entry;
> -
> -	return entry->attachment_uid++;
> -}
>   #else
>   
>   static inline int dma_buf_init_sysfs_statistics(void)
> @@ -44,19 +29,7 @@ static inline int dma_buf_stats_setup(struct dma_buf *dmabuf)
>   {
>   	return 0;
>   }
> -static inline int dma_buf_attach_stats_setup(struct dma_buf_attachment *attach,
> -					     unsigned int uid)
> -{
> -	return 0;
> -}
>   
>   static inline void dma_buf_stats_teardown(struct dma_buf *dmabuf) {}
> -static inline void dma_buf_attach_stats_teardown(struct dma_buf_attachment *attach) {}
> -static inline void dma_buf_update_attachment_map_count(struct dma_buf_attachment *attach,
> -						       int delta) {}
> -static inline unsigned int dma_buf_update_attach_uid(struct dma_buf *dmabuf)
> -{
> -	return 0;
> -}
>   #endif
>   #endif // _DMA_BUF_SYSFS_STATS_H
> diff --git a/drivers/dma-buf/dma-buf.c b/drivers/dma-buf/dma-buf.c
> index 510b42771974..b1a6db71c656 100644
> --- a/drivers/dma-buf/dma-buf.c
> +++ b/drivers/dma-buf/dma-buf.c
> @@ -738,7 +738,6 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
>   {
>   	struct dma_buf_attachment *attach;
>   	int ret;
> -	unsigned int attach_uid;
>   
>   	if (WARN_ON(!dmabuf || !dev))
>   		return ERR_PTR(-EINVAL);
> @@ -764,13 +763,8 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
>   	}
>   	dma_resv_lock(dmabuf->resv, NULL);
>   	list_add(&attach->node, &dmabuf->attachments);
> -	attach_uid = dma_buf_update_attach_uid(dmabuf);
>   	dma_resv_unlock(dmabuf->resv);
>   
> -	ret = dma_buf_attach_stats_setup(attach, attach_uid);
> -	if (ret)
> -		goto err_sysfs;
> -
>   	/* When either the importer or the exporter can't handle dynamic
>   	 * mappings we cache the mapping here to avoid issues with the
>   	 * reservation object lock.
> @@ -797,7 +791,6 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
>   			dma_resv_unlock(attach->dmabuf->resv);
>   		attach->sgt = sgt;
>   		attach->dir = DMA_BIDIRECTIONAL;
> -		dma_buf_update_attachment_map_count(attach, 1 /* delta */);
>   	}
>   
>   	return attach;
> @@ -814,7 +807,6 @@ dma_buf_dynamic_attach(struct dma_buf *dmabuf, struct device *dev,
>   	if (dma_buf_is_dynamic(attach->dmabuf))
>   		dma_resv_unlock(attach->dmabuf->resv);
>   
> -err_sysfs:
>   	dma_buf_detach(dmabuf, attach);
>   	return ERR_PTR(ret);
>   }
> @@ -864,7 +856,6 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
>   			dma_resv_lock(attach->dmabuf->resv, NULL);
>   
>   		__unmap_dma_buf(attach, attach->sgt, attach->dir);
> -		dma_buf_update_attachment_map_count(attach, -1 /* delta */);
>   
>   		if (dma_buf_is_dynamic(attach->dmabuf)) {
>   			dmabuf->ops->unpin(attach);
> @@ -878,7 +869,6 @@ void dma_buf_detach(struct dma_buf *dmabuf, struct dma_buf_attachment *attach)
>   	if (dmabuf->ops->detach)
>   		dmabuf->ops->detach(dmabuf, attach);
>   
> -	dma_buf_attach_stats_teardown(attach);
>   	kfree(attach);
>   }
>   EXPORT_SYMBOL_GPL(dma_buf_detach);
> @@ -1020,10 +1010,6 @@ struct sg_table *dma_buf_map_attachment(struct dma_buf_attachment *attach,
>   		}
>   	}
>   #endif /* CONFIG_DMA_API_DEBUG */
> -
> -	if (!IS_ERR(sg_table))
> -		dma_buf_update_attachment_map_count(attach, 1 /* delta */);
> -
>   	return sg_table;
>   }
>   EXPORT_SYMBOL_GPL(dma_buf_map_attachment);
> @@ -1061,8 +1047,6 @@ void dma_buf_unmap_attachment(struct dma_buf_attachment *attach,
>   	if (dma_buf_is_dynamic(attach->dmabuf) &&
>   	    !IS_ENABLED(CONFIG_DMABUF_MOVE_NOTIFY))
>   		dma_buf_unpin(attach);
> -
> -	dma_buf_update_attachment_map_count(attach, -1 /* delta */);
>   }
>   EXPORT_SYMBOL_GPL(dma_buf_unmap_attachment);
>   
> diff --git a/include/linux/dma-buf.h b/include/linux/dma-buf.h
> index 2b814fde0d11..678b2006be78 100644
> --- a/include/linux/dma-buf.h
> +++ b/include/linux/dma-buf.h
> @@ -444,15 +444,6 @@ struct dma_buf {
>   	struct dma_buf_sysfs_entry {
>   		struct kobject kobj;
>   		struct dma_buf *dmabuf;
> -
> -		/**
> -		 * @sysfs_entry.attachment_uid:
> -		 *
> -		 * This is protected by the dma_resv_lock() on @resv and is
> -		 * incremented on each attach.
> -		 */
> -		unsigned int attachment_uid;
> -		struct kset *attach_stats_kset;
>   	} *sysfs_entry;
>   #endif
>   };
> @@ -504,7 +495,6 @@ struct dma_buf_attach_ops {
>    * @importer_ops: importer operations for this attachment, if provided
>    * dma_buf_map/unmap_attachment() must be called with the dma_resv lock held.
>    * @importer_priv: importer specific attachment data.
> - * @sysfs_entry: For exposing information about this attachment in sysfs.
>    *
>    * This structure holds the attachment information between the dma_buf buffer
>    * and its user device(s). The list contains one attachment struct per device
> @@ -525,13 +515,6 @@ struct dma_buf_attachment {
>   	const struct dma_buf_attach_ops *importer_ops;
>   	void *importer_priv;
>   	void *priv;
> -#ifdef CONFIG_DMABUF_SYSFS_STATS
> -	/* for sysfs stats */
> -	struct dma_buf_attach_sysfs_entry {
> -		struct kobject kobj;
> -		unsigned int map_counter;
> -	} *sysfs_entry;
> -#endif
>   };
>   
>   /**