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Subject[PATCH] dma-buf: Delete the DMA-BUF attachment sysfs statistics
From
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@google.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@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
};

/**
--
2.32.0.93.g670b81a890-goog
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