[PATCH 3/6] drm: add unified vma offset manager
Daniel Vetter
daniel at ffwll.ch
Mon Jul 1 12:42:25 PDT 2013
On Mon, Jul 01, 2013 at 08:33:00PM +0200, David Herrmann wrote:
> If we want to map GPU memory into user-space, we need to linearize the
> addresses to not confuse mm-core. Currently, GEM and TTM both implement
> their own offset-managers to assign a pgoff to each object for user-space
> CPU access. GEM uses a hash-table, TTM uses an rbtree.
>
> This patch provides a unified implementation that can be used to replace
> both. TTM allows partial mmaps with a given offset, so we cannot use
> hashtables as the start address may not be known at mmap time. Hence, we
> use the rbtree-implementation of TTM.
>
> We could easily update drm_mm to use an rbtree instead of a linked list
> for it's object list and thus drop the rbtree from the vma-manager.
> However, this would slow down drm_mm object allocation for all other
> use-cases (rbtree insertion) and add another 4-8 bytes to each mm node.
> Hence, use the separate tree but allow for later migration.
>
> This is a rewrite of the 2012-proposal by David Airlie <airlied at linux.ie>
>
> Signed-off-by: David Herrmann <dh.herrmann at gmail.com>
This seems to sprinkle a lot of likely/unlikely. Imo those are only
justified in two cases:
- When we have real performance data proving that they're worth it.
- Sometimes they're also useful as self-documenting code for the truly
unlikely. But early do-nothing returns and error handling are
established code patterns, so imo don't qualify.
I think none of the likely/unlikely below qualify, so imo better to remove
them.
Second high-level review request: Can you please convert the very nice
documentation you already added into proper kerneldoc and link it up at an
appropriate section in the drm DocBook?
A few more comments below. I'll postpone reviewing the gem/ttm conversion
patches until this is settled a bit.
> ---
> drivers/gpu/drm/Makefile | 2 +-
> drivers/gpu/drm/drm_vma_manager.c | 224 ++++++++++++++++++++++++++++++++++++++
> include/drm/drm_vma_manager.h | 107 ++++++++++++++++++
> 3 files changed, 332 insertions(+), 1 deletion(-)
> create mode 100644 drivers/gpu/drm/drm_vma_manager.c
> create mode 100644 include/drm/drm_vma_manager.h
>
> diff --git a/drivers/gpu/drm/Makefile b/drivers/gpu/drm/Makefile
> index 1c9f2439..f8851cc 100644
> --- a/drivers/gpu/drm/Makefile
> +++ b/drivers/gpu/drm/Makefile
> @@ -12,7 +12,7 @@ drm-y := drm_auth.o drm_buffer.o drm_bufs.o drm_cache.o \
> drm_platform.o drm_sysfs.o drm_hashtab.o drm_mm.o \
> drm_crtc.o drm_modes.o drm_edid.o \
> drm_info.o drm_debugfs.o drm_encoder_slave.o \
> - drm_trace_points.o drm_global.o drm_prime.o
> + drm_trace_points.o drm_global.o drm_prime.o drm_vma_manager.o
>
> drm-$(CONFIG_COMPAT) += drm_ioc32.o
> drm-$(CONFIG_DRM_GEM_CMA_HELPER) += drm_gem_cma_helper.o
> diff --git a/drivers/gpu/drm/drm_vma_manager.c b/drivers/gpu/drm/drm_vma_manager.c
> new file mode 100644
> index 0000000..c28639f
> --- /dev/null
> +++ b/drivers/gpu/drm/drm_vma_manager.c
> @@ -0,0 +1,224 @@
> +/*
> + * Copyright (c) 2012 David Airlie <airlied at linux.ie>
> + * Copyright (c) 2013 David Herrmann <dh.herrmann at gmail.com>
> + *
> + * Permission is hereby granted, free of charge, to any person obtaining a
> + * copy of this software and associated documentation files (the "Software"),
> + * to deal in the Software without restriction, including without limitation
> + * the rights to use, copy, modify, merge, publish, distribute, sublicense,
> + * and/or sell copies of the Software, and to permit persons to whom the
> + * Software is furnished to do so, subject to the following conditions:
> + *
> + * The above copyright notice and this permission notice shall be included in
> + * all copies or substantial portions of the Software.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
> + * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
> + * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
> + * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
> + * OTHER DEALINGS IN THE SOFTWARE.
> + */
> +
> +#include <drm/drmP.h>
> +#include <drm/drm_mm.h>
> +#include <drm/drm_vma_manager.h>
> +#include <linux/mm.h>
> +#include <linux/module.h>
> +#include <linux/rbtree.h>
> +#include <linux/slab.h>
> +#include <linux/spinlock.h>
> +#include <linux/types.h>
> +
> +/** @file drm_vma_manager.c
> + *
> + * The vma-manager is responsible to map arbitrary driver-dependent memory
> + * regions into the linear user address-space. It provides offsets to the
> + * caller which can then be used on the address_space of the drm-device. It
> + * takes care to not overlap regions, size them appropriately and to not
> + * confuse mm-core by inconsistent fake vm_pgoff fields.
> + *
> + * We use drm_mm as backend to manage object allocations. But it is highly
> + * optimized for alloc/free calls, not lookups. Hence, we use an rb-tree to
> + * speed up offset lookups.
> + */
> +
> +/** drm_vma_offset_manager_init()
> + *
> + * Initialize a new offset-manager. The offset and area size available for the
> + * manager are given as @page_offset and @size. Both are interpreted as
> + * page-numbers, not bytes.
> + *
> + * Adding/removing nodes from the manager is locked internally and protected
> + * against concurrent access. However, node allocation and destruction is left
> + * for the caller. While calling into the vma-manager, a given node must
> + * always be guaranteed to be referenced.
> + */
> +void drm_vma_offset_manager_init(struct drm_vma_offset_manager *mgr,
> + unsigned long page_offset, unsigned long size)
> +{
> + rwlock_init(&mgr->vm_lock);
> + mgr->vm_addr_space_rb = RB_ROOT;
> + drm_mm_init(&mgr->vm_addr_space_mm, page_offset, size);
> +}
> +EXPORT_SYMBOL(drm_vma_offset_manager_init);
> +
> +/** drm_vma_offset_manager_destroy()
> + *
> + * Destroy an object manager which was previously created via
> + * drm_vma_offset_manager_init(). The caller must remove all allocated nodes
> + * before destroying the manager. Otherwise, drm_mm will refuse to free the
> + * requested resources.
> + *
> + * The manager must not be accessed after this function is called.
> + */
> +void drm_vma_offset_manager_destroy(struct drm_vma_offset_manager *mgr)
> +{
> + BUG_ON(!drm_mm_clean(&mgr->vm_addr_space_mm));
Please convert this to a WARN_ON - drm_mm has code to cobble over buggy
drivers, and killing the driver with a BUG_ON if we could keep on going
with just a WARN_ON is a real pain for development.
> +
> + /* take the lock to protect against buggy drivers */
> + write_lock(&mgr->vm_lock);
> + drm_mm_takedown(&mgr->vm_addr_space_mm);
> + write_unlock(&mgr->vm_lock);
> +}
> +EXPORT_SYMBOL(drm_vma_offset_manager_destroy);
> +
> +/** drm_vma_offset_lookup()
> + *
> + * Find a node given a start address and object size. This returns the _best_
> + * match for the given node. That is, @start may point somewhere into a valid
> + * region and the given node will be returned, as long as the node spans the
> + * whole requested area (given the size in number of pages as @pages).
> + *
> + * Returns NULL if no suitable node can be found. Otherwise, the best match
> + * is returned. It's the caller's responsibility to make sure the node doesn't
> + * get destroyed before the caller can access it.
> + */
> +struct drm_vma_offset_node *drm_vma_offset_lookup(struct drm_vma_offset_manager *mgr,
> + unsigned long start,
> + unsigned long pages)
> +{
> + struct drm_vma_offset_node *node, *best;
> + struct rb_node *iter;
> + unsigned long offset;
> +
> + read_lock(&mgr->vm_lock);
> +
> + iter = mgr->vm_addr_space_rb.rb_node;
> + best = NULL;
> +
> + while (likely(iter)) {
> + node = rb_entry(iter, struct drm_vma_offset_node, vm_rb);
> + offset = node->vm_node.start;
> + if (start >= offset) {
> + iter = iter->rb_right;
> + best = node;
> + if (start == offset)
> + break;
> + } else {
> + iter = iter->rb_left;
> + }
> + }
> +
> + /* verify that the node spans the requested area */
> + if (likely(best)) {
> + offset = best->vm_node.start + best->vm_pages;
> + if (offset > start + pages)
> + best = NULL;
> + }
> +
> + read_unlock(&mgr->vm_lock);
> +
> + return best;
> +}
> +EXPORT_SYMBOL(drm_vma_offset_lookup);
> +
> +/* internal helper to link @node into the rb-tree */
> +static void _drm_vma_offset_add_rb(struct drm_vma_offset_manager *mgr,
> + struct drm_vma_offset_node *node)
> +{
> + struct rb_node **iter = &mgr->vm_addr_space_rb.rb_node;
> + struct rb_node *parent = NULL;
> + struct drm_vma_offset_node *iter_node;
> +
> + while (likely(*iter)) {
> + parent = *iter;
> + iter_node = rb_entry(*iter, struct drm_vma_offset_node, vm_rb);
> +
> + if (node->vm_node.start < iter_node->vm_node.start)
> + iter = &(*iter)->rb_left;
> + else if (node->vm_node.start > iter_node->vm_node.start)
> + iter = &(*iter)->rb_right;
> + else
> + BUG();
> + }
> +
> + rb_link_node(&node->vm_rb, parent, iter);
> + rb_insert_color(&node->vm_rb, &mgr->vm_addr_space_rb);
> +}
> +
> +/** drm_vma_offset_add()
> + *
> + * Add a node to the offset-manager. If the node was already added, this does
> + * nothing and return 0. @pages is the size of the object given in number of
> + * pages.
> + * After this call succeeds, you can access the offset of the node until it
> + * is removed again.
> + *
> + * If this call fails, it is safe to retry the operation or call
> + * drm_vma_offset_remove(), anyway. However, no cleanup is required in that
> + * case.
> + */
> +int drm_vma_offset_add(struct drm_vma_offset_manager *mgr,
> + struct drm_vma_offset_node *node, unsigned long pages)
> +{
> + int ret;
> +
> + write_lock(&mgr->vm_lock);
> +
> + if (unlikely(drm_mm_node_linked(&node->vm_node))) {
> + ret = 0;
> + goto out_unlock;
> + }
> +
> + ret = drm_mm_insert_node_generic(&mgr->vm_addr_space_mm,
> + &node->vm_node, pages, 0, 0);
This allocates memory, so potentially blocks. This doesn't mesh well with
the spinning rwlock (lockdep should seriously complain about this btw).
Please use an rwsemaphore instead.
> + if (unlikely(ret))
> + goto out_reset;
> +
> + node->vm_pages = pages;
> + _drm_vma_offset_add_rb(mgr, node);
> + goto out_unlock;
> +
> +out_reset:
> + /* we don't know what happened to @node->vm_node, so clear it */
> + drm_vma_node_reset(node);
If you switch over to drm_mm_node_allocated then this reset could
shouldn't be required - it'd be a pretty serious bug in drm_mm.c
> +out_unlock:
> + write_unlock(&mgr->vm_lock);
> + return ret;
> +}
> +EXPORT_SYMBOL(drm_vma_offset_add);
> +
> +/** drm_vma_offset_remove()
> + *
> + * Remove a node from the offset manager. If the node wasn't added before, this
> + * does nothing. After this call returns, the offset of the node must be not
> + * accessed, anymore.
> + * It is safe to add the node via drm_vma_offset_add() again.
> + */
> +void drm_vma_offset_remove(struct drm_vma_offset_manager *mgr,
> + struct drm_vma_offset_node *node)
> +{
> + if (unlikely(!drm_mm_node_linked(&node->vm_node)))
> + return;
> +
> + write_lock(&mgr->vm_lock);
> +
> + rb_erase(&node->vm_rb, &mgr->vm_addr_space_rb);
> + drm_mm_remove_node(&node->vm_node);
> + drm_vma_node_reset(node);
> +
> + write_unlock(&mgr->vm_lock);
> +}
> +EXPORT_SYMBOL(drm_vma_offset_remove);
> diff --git a/include/drm/drm_vma_manager.h b/include/drm/drm_vma_manager.h
> new file mode 100644
> index 0000000..8a1975c
> --- /dev/null
> +++ b/include/drm/drm_vma_manager.h
> @@ -0,0 +1,107 @@
> +#ifndef __DRM_VMA_MANAGER_H__
> +#define __DRM_VMA_MANAGER_H__
> +
> +/*
> + * Copyright (c) 2013 David Herrmann <dh.herrmann at gmail.com>
> + *
> + * Permission is hereby granted, free of charge, to any person obtaining a
> + * copy of this software and associated documentation files (the "Software"),
> + * to deal in the Software without restriction, including without limitation
> + * the rights to use, copy, modify, merge, publish, distribute, sublicense,
> + * and/or sell copies of the Software, and to permit persons to whom the
> + * Software is furnished to do so, subject to the following conditions:
> + *
> + * The above copyright notice and this permission notice shall be included in
> + * all copies or substantial portions of the Software.
> + *
> + * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
> + * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
> + * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
> + * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
> + * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
> + * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
> + * OTHER DEALINGS IN THE SOFTWARE.
> + */
> +
> +#include <drm/drmP.h>
> +#include <drm/drm_mm.h>
> +#include <linux/module.h>
> +#include <linux/rbtree.h>
> +#include <linux/spinlock.h>
> +#include <linux/types.h>
> +
> +struct drm_vma_offset_node {
> + struct drm_mm_node vm_node;
> + struct rb_node vm_rb;
> + unsigned long vm_pages;
> +};
> +
> +struct drm_vma_offset_manager {
> + rwlock_t vm_lock;
> + struct rb_root vm_addr_space_rb;
> + struct drm_mm vm_addr_space_mm;
> +};
> +
> +void drm_vma_offset_manager_init(struct drm_vma_offset_manager *mgr,
> + unsigned long page_offset, unsigned long size);
> +void drm_vma_offset_manager_destroy(struct drm_vma_offset_manager *mgr);
> +
> +struct drm_vma_offset_node *drm_vma_offset_lookup(struct drm_vma_offset_manager *mgr,
> + unsigned long start,
> + unsigned long pages);
> +int drm_vma_offset_add(struct drm_vma_offset_manager *mgr,
> + struct drm_vma_offset_node *node, unsigned long pages);
> +void drm_vma_offset_remove(struct drm_vma_offset_manager *mgr,
> + struct drm_vma_offset_node *node);
> +
> +/** drm_vma_offset_exact_lookup()
> + *
> + * Same as drm_vma_offset_lookup() but does not allow any offset but only
> + * returns the exact object with the given start address.
> + */
> +static inline struct drm_vma_offset_node *
> +drm_vma_offset_exact_lookup(struct drm_vma_offset_manager *mgr,
> + unsigned long start)
> +{
> + return drm_vma_offset_lookup(mgr, start, 1);
> +}
> +
> +/** drm_vma_node_reset()
> + *
> + * Reset a node to its initial state.
> + */
> +static inline void drm_vma_node_reset(struct drm_vma_offset_node *node)
> +{
> + memset(&node->vm_node, 0, sizeof(node->vm_node));
> +}
> +
> +/** drm_vma_node_start()
> + *
> + * Return the start address of the given node as pfn.
> + */
> +static inline unsigned long drm_vma_node_start(struct drm_vma_offset_node *node)
> +{
> + return node->vm_node.start;
> +}
> +
> +/** drm_vma_node_has_offset()
> + *
> + * Return true iff the node was previously allocated an offset and added to
> + * an vma offset manager.
> + */
> +static inline bool drm_vma_node_has_offset(struct drm_vma_offset_node *node)
> +{
> + return drm_mm_node_linked(&node->vm_node);
> +}
> +
> +/** drm_vma_node_offset_addr()
> + *
> + * Same as drm_vma_node_start() but returns the address as a valid userspace
> + * address (instead of a pfn).
> + */
Userspace address and pfn are a bit misleading imo in this context. I'd go
with "byte offset for consumption by userspace/mmap" and "page-based
addressing" or something similar.
> +static inline __u64 drm_vma_node_offset_addr(struct drm_vma_offset_node *node)
> +{
> + return ((__u64)node->vm_node.start) << PAGE_SHIFT;
> +}
> +
> +#endif /* __DRM_VMA_MANAGER_H__ */
> --
> 1.8.3.2
>
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--
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch
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