[RFC PATCH] drm: rework flip-work helpers to avoid calling func when the FIFO is full
Boris BREZILLON
boris.brezillon at free-electrons.com
Fri Jul 11 08:17:01 PDT 2014
Make use of lists instead of kfifo in order to dynamically allocate
task entry when someone require some delayed work, and thus preventing
drm_flip_work_queue from directly calling func instead of queuing this
call.
This allow drm_flip_work_queue to be safely called even within irq
handlers.
Add new helper functions to allocate a flip work task and queue it when
needed. This prevents allocating data within irq context (which might
impact the time spent in the irq handler).
Signed-off-by: Boris BREZILLON <boris.brezillon at free-electrons.com>
---
Hi Rob,
This is a proposal for what you suggested (dynamically growing the drm
flip work queue in order to avoid direct call of work->func when calling
drm_flip_work_queue).
I'm not sure this is exactly what you expected, because I'm now using
lists instead of kfifo (and thus lose the lockless part), but at least
we can now safely call drm_flip_work_queue or drm_flip_work_queue_task
from irq handlers :-).
You were also worried about queueing the same framebuffer multiple times
and with this implementation you shouldn't have any problem (at least with
drm_flip_work_queue, what people do with drm_flip_work_queue_task is their
own responsability, but they should allocate one task for each operation
even if they are manipulating the same framebuffer).
This is just a suggestion, so don't hesitate to tell me that it doesn't
match your expectations.
Best Regards,
Boris
drivers/gpu/drm/drm_flip_work.c | 95 ++++++++++++++++++++++++++++++-----------
include/drm/drm_flip_work.h | 29 +++++++++----
2 files changed, 92 insertions(+), 32 deletions(-)
diff --git a/drivers/gpu/drm/drm_flip_work.c b/drivers/gpu/drm/drm_flip_work.c
index f9c7fa3..21d5715 100644
--- a/drivers/gpu/drm/drm_flip_work.c
+++ b/drivers/gpu/drm/drm_flip_work.c
@@ -25,6 +25,43 @@
#include "drm_flip_work.h"
/**
+ * drm_flip_work_allocate_task - allocate a flip-work task
+ * @data: data associated to the task
+ *
+ * Allocate a drm_flip_task object and attach private data to it.
+ */
+struct drm_flip_task *drm_flip_work_allocate_task(void *data)
+{
+ struct drm_flip_task *task;
+
+ task = kzalloc(sizeof(*task), GFP_KERNEL);
+ if (task)
+ task->data = data;
+
+ return task;
+}
+EXPORT_SYMBOL(drm_flip_work_allocate_task);
+
+/**
+ * drm_flip_work_queue_task - queue a specific task
+ * @work: the flip-work
+ * @task: the task to handle
+ *
+ * Queues task, that will later be run (passed back to drm_flip_func_t
+ * func) on a work queue after drm_flip_work_commit() is called.
+ */
+void drm_flip_work_queue_task(struct drm_flip_work *work,
+ struct drm_flip_task *task)
+{
+ unsigned long flags;
+
+ spin_lock_irqsave(&work->lock, flags);
+ list_add_tail(&task->node, &work->queued);
+ spin_unlock_irqrestore(&work->lock, flags);
+}
+EXPORT_SYMBOL(drm_flip_work_queue_task);
+
+/**
* drm_flip_work_queue - queue work
* @work: the flip-work
* @val: the value to queue
@@ -34,10 +71,14 @@
*/
void drm_flip_work_queue(struct drm_flip_work *work, void *val)
{
- if (kfifo_put(&work->fifo, val)) {
- atomic_inc(&work->pending);
+ struct drm_flip_task *task;
+
+ task = kzalloc(sizeof(*task), GFP_KERNEL);
+ if (task) {
+ task->data = val;
+ drm_flip_work_queue_task(work, task);
} else {
- DRM_ERROR("%s fifo full!\n", work->name);
+ DRM_ERROR("%s could not allocate task!\n", work->name);
work->func(work, val);
}
}
@@ -56,9 +97,12 @@ EXPORT_SYMBOL(drm_flip_work_queue);
void drm_flip_work_commit(struct drm_flip_work *work,
struct workqueue_struct *wq)
{
- uint32_t pending = atomic_read(&work->pending);
- atomic_add(pending, &work->count);
- atomic_sub(pending, &work->pending);
+ unsigned long flags;
+
+ spin_lock_irqsave(&work->lock, flags);
+ list_splice_tail(&work->queued, &work->commited);
+ INIT_LIST_HEAD(&work->queued);
+ spin_unlock_irqrestore(&work->lock, flags);
queue_work(wq, &work->worker);
}
EXPORT_SYMBOL(drm_flip_work_commit);
@@ -66,14 +110,26 @@ EXPORT_SYMBOL(drm_flip_work_commit);
static void flip_worker(struct work_struct *w)
{
struct drm_flip_work *work = container_of(w, struct drm_flip_work, worker);
- uint32_t count = atomic_read(&work->count);
- void *val = NULL;
+ struct list_head tasks;
+ unsigned long flags;
- atomic_sub(count, &work->count);
+ while (1) {
+ struct drm_flip_task *task, *tmp;
- while(count--)
- if (!WARN_ON(!kfifo_get(&work->fifo, &val)))
- work->func(work, val);
+ INIT_LIST_HEAD(&tasks);
+ spin_lock_irqsave(&work->lock, flags);
+ list_splice_tail(&work->commited, &tasks);
+ INIT_LIST_HEAD(&work->commited);
+ spin_unlock_irqrestore(&work->lock, flags);
+
+ if (list_empty(&tasks))
+ break;
+
+ list_for_each_entry_safe(task, tmp, &tasks, node) {
+ work->func(work, task->data);
+ kfree(task);
+ }
+ }
}
/**
@@ -91,19 +147,11 @@ static void flip_worker(struct work_struct *w)
int drm_flip_work_init(struct drm_flip_work *work, int size,
const char *name, drm_flip_func_t func)
{
- int ret;
-
work->name = name;
- atomic_set(&work->count, 0);
- atomic_set(&work->pending, 0);
+ INIT_LIST_HEAD(&work->queued);
+ INIT_LIST_HEAD(&work->commited);
work->func = func;
- ret = kfifo_alloc(&work->fifo, size, GFP_KERNEL);
- if (ret) {
- DRM_ERROR("could not allocate %s fifo\n", name);
- return ret;
- }
-
INIT_WORK(&work->worker, flip_worker);
return 0;
@@ -118,7 +166,6 @@ EXPORT_SYMBOL(drm_flip_work_init);
*/
void drm_flip_work_cleanup(struct drm_flip_work *work)
{
- WARN_ON(!kfifo_is_empty(&work->fifo));
- kfifo_free(&work->fifo);
+ WARN_ON(!list_empty(&work->queued) || !list_empty(&work->commited));
}
EXPORT_SYMBOL(drm_flip_work_cleanup);
diff --git a/include/drm/drm_flip_work.h b/include/drm/drm_flip_work.h
index 9eed34d..549981f 100644
--- a/include/drm/drm_flip_work.h
+++ b/include/drm/drm_flip_work.h
@@ -25,6 +25,7 @@
#define DRM_FLIP_WORK_H
#include <linux/kfifo.h>
+#include <linux/spinlock.h>
#include <linux/workqueue.h>
/**
@@ -32,9 +33,7 @@
*
* Util to queue up work to run from work-queue context after flip/vblank.
* Typically this can be used to defer unref of framebuffer's, cursor
- * bo's, etc until after vblank. The APIs are all safe (and lockless)
- * for up to one producer and once consumer at a time. The single-consumer
- * aspect is ensured by committing the queued work to a single work-queue.
+ * bo's, etc until after vblank. The APIs are all safe.
*/
struct drm_flip_work;
@@ -51,22 +50,36 @@ struct drm_flip_work;
typedef void (*drm_flip_func_t)(struct drm_flip_work *work, void *val);
/**
+ * struct drm_flip_task - flip work task
+ * @node: list entry element
+ * @data: data to pass to work->func
+ */
+struct drm_flip_task {
+ struct list_head node;
+ void *data;
+};
+
+/**
* struct drm_flip_work - flip work queue
* @name: debug name
- * @pending: number of queued but not committed items
- * @count: number of committed items
* @func: callback fxn called for each committed item
* @worker: worker which calls @func
- * @fifo: queue of committed items
+ * @queued: queued tasks
+ * @commited: commited tasks
+ * @lock: lock to access queued and commited lists
*/
struct drm_flip_work {
const char *name;
- atomic_t pending, count;
drm_flip_func_t func;
struct work_struct worker;
- DECLARE_KFIFO_PTR(fifo, void *);
+ struct list_head queued;
+ struct list_head commited;
+ spinlock_t lock;
};
+struct drm_flip_task *drm_flip_work_allocate_task(void *data);
+void drm_flip_work_queue_task(struct drm_flip_work *work,
+ struct drm_flip_task *task);
void drm_flip_work_queue(struct drm_flip_work *work, void *val);
void drm_flip_work_commit(struct drm_flip_work *work,
struct workqueue_struct *wq);
--
1.8.3.2
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