Message-Id: <20210710051027.42828-1-hridya@google.com>
Date:   Fri,  9 Jul 2021 22:10:24 -0700
From:   Hridya Valsaraju <hridya@...gle.com>
To:     daniel@...ll.ch, Sumit Semwal <sumit.semwal@...aro.org>,
        "Christian König" <christian.koenig@....com>,
        Hridya Valsaraju <hridya@...gle.com>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, linaro-mm-sig@...ts.linaro.org
Cc:     kernel-team@...roid.com, john.stultz@...aro.org, surenb@...gle.com
Subject: [PATCH] dma-buf: Delete the DMA-BUF attachment sysfs statistics

The DMA-BUF attachment statistics form a subset of the DMA-BUF
sysfs statistics that recently merged to the drm-misc tree.
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@...gle.com>
---

Hello all,

One of our partners recently reported a perf regression in a driver
which was being caused due to the overhead of setup/teardown of the
sysfs attachment statistics in the dma_buf_attach()/dma_buf_detach()
invocations. Since the driver's latency requirements were of the order
of microseconds(~100us), the overhead was significant.
Since this indicates that the solution might not work well for
all DMA-BUF importers, I think the right thing to do might be to delete
the same before it reaches upstream and becomes ABI :( I apologize for
the inconvenience.

This patch is based on the drm-misc-next branch. Please feel free to
let me know if you would prefer that I send a full revert and new patch that
adds the rest of the statistics.

Regards,
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@...gle.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@...gle.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@...gle.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@...gle.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@...gle.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
 };
 
 /**
-- 
2.32.0.93.g670b81a890-goog

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