Re: [PATCH v14 52/56] media: core: Add bitmap manage bufs array entries

Benjamin Gaignard
2023-11-08T15:30:48Z

Le 08/11/2023 à 11:44, Tomasz Figa a écrit :
> On Tue, Oct 31, 2023 at 05:31:00PM +0100, Benjamin Gaignard wrote:
>> Add a bitmap field to know which of bufs array entries are
>> used or not.
>> Remove no more used num_buffers field from queue structure.
>> Use bitmap_find_next_zero_area() to find the first possible
>> range when creating new buffers to fill the gaps.
>>
>> Signed-off-by: Benjamin Gaignard <benjamin.gaignard@collabora.com>
>> ---
>> .../media/common/videobuf2/videobuf2-core.c | 42 +++++++++++++++----
>> include/media/videobuf2-core.h | 15 ++++---
>> 2 files changed, 42 insertions(+), 15 deletions(-)
>>
>> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
>> index 2c8cf479a962..6e88406fcae9 100644
>> --- a/drivers/media/common/videobuf2/videobuf2-core.c
>> +++ b/drivers/media/common/videobuf2/videobuf2-core.c
>> @@ -416,11 +416,12 @@ static void init_buffer_cache_hints(struct vb2_queue *q, struct vb2_buffer *vb)
>> */
>> static void vb2_queue_add_buffer(struct vb2_queue *q, struct vb2_buffer *vb, unsigned int index)
>> {
>> - WARN_ON(index >= q->max_num_buffers || q->bufs[index]);
>> + WARN_ON(index >= q->max_num_buffers || test_bit(index, q->bufs_bitmap));
>>
>> q->bufs[index] = vb;
>> vb->index = index;
>> vb->vb2_queue = q;
>> + set_bit(index, q->bufs_bitmap);
>> }
>>
>> /**
>> @@ -429,6 +430,7 @@ static void vb2_queue_add_buffer(struct vb2_queue *q, struct vb2_buffer *vb, uns
>> */
>> static void vb2_queue_remove_buffer(struct vb2_buffer *vb)
>> {
>> + clear_bit(vb->index, vb->vb2_queue->bufs_bitmap);
>> vb->vb2_queue->bufs[vb->index] = NULL;
>> vb->vb2_queue = NULL;
>> }
>> @@ -450,11 +452,12 @@ static int __vb2_queue_alloc(struct vb2_queue *q, enum vb2_memory memory,
>> unsigned long index;
>> int ret;
>>
>> - /* Ensure that the number of already queue + num_buffers is below q->max_num_buffers */
>> + /* Ensure that vb2_get_num_buffers(q) + num_buffers is no more than q->max_num_buffers */
>> num_buffers = min_t(unsigned int, num_buffers,
>> q->max_num_buffers - vb2_get_num_buffers(q));
>>
>> - index = vb2_get_num_buffers(q);
>> + index = bitmap_find_next_zero_area(q->bufs_bitmap, q->max_num_buffers,
>> + 0, num_buffers, 0);
>>
>> *first_index = index;
>>
>> @@ -656,7 +659,6 @@ static void __vb2_queue_free(struct vb2_queue *q, unsigned int buffers)
>> kfree(vb);
>> }
>>
>> - q->num_buffers -= buffers;
>> if (!vb2_get_num_buffers(q)) {
>> q->memory = VB2_MEMORY_UNKNOWN;
>> INIT_LIST_HEAD(&q->queued_list);
>> @@ -874,6 +876,14 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory,
>> q->bufs = kcalloc(q->max_num_buffers, sizeof(*q->bufs), GFP_KERNEL);
>> if (!q->bufs)
>> ret = -ENOMEM;
>> +
>> + if (!q->bufs_bitmap)
>> + q->bufs_bitmap = bitmap_zalloc(q->max_num_buffers, GFP_KERNEL);
>> + if (!q->bufs_bitmap) {
>> + ret = -ENOMEM;
>> + kfree(q->bufs);
>> + q->bufs = NULL;
>> + }
>> q->memory = memory;
>> mutex_unlock(&q->mmap_lock);
>> if (ret)
>> @@ -943,7 +953,6 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory,
>> }
>>
>> mutex_lock(&q->mmap_lock);
>> - q->num_buffers = allocated_buffers;
>>
>> if (ret < 0) {
>> /*
>> @@ -970,6 +979,10 @@ int vb2_core_reqbufs(struct vb2_queue *q, enum vb2_memory memory,
>> mutex_lock(&q->mmap_lock);
>> q->memory = VB2_MEMORY_UNKNOWN;
>> mutex_unlock(&q->mmap_lock);
>> + kfree(q->bufs);
>> + q->bufs = NULL;
>> + bitmap_free(q->bufs_bitmap);
>> + q->bufs_bitmap = NULL;
>> return ret;
>> }
>> EXPORT_SYMBOL_GPL(vb2_core_reqbufs);
>> @@ -1006,9 +1019,19 @@ int vb2_core_create_bufs(struct vb2_queue *q, enum vb2_memory memory,
>> q->memory = memory;
>> if (!q->bufs)
>> q->bufs = kcalloc(q->max_num_buffers, sizeof(*q->bufs), GFP_KERNEL);
>> - if (!q->bufs)
>> + if (!q->bufs) {
>> ret = -ENOMEM;
>> + goto unlock;
>> + }
>> + if (!q->bufs_bitmap)
>> + q->bufs_bitmap = bitmap_zalloc(q->max_num_buffers, GFP_KERNEL);
> Same as with the kcalloc(). Why not just allocate this in the core code,
> e.g. vb2_core_queue_init()?
>
> Actually, is it because we want to avoid allocating
> resources early, before the need to actually use the vb2 queue?
> If so, could this go to some other core function that runs later, e.g. __vb2_queue_alloc()?

For the same reason :-)
vb2_core_queue_init() and vb2_core_queue_release() aren't balanced so I can't use them for that.

>
>> + if (!q->bufs_bitmap) {
>> + ret = -ENOMEM;
>> + kfree(q->bufs);
>> + q->bufs = NULL;
>> + }
>> mutex_unlock(&q->mmap_lock);
>> +unlock:
>> if (ret)
>> return ret;
>> q->waiting_for_buffers = !q->is_output;
>> @@ -1070,7 +1093,6 @@ int vb2_core_create_bufs(struct vb2_queue *q, enum vb2_memory memory,
>> }
>>
>> mutex_lock(&q->mmap_lock);
>> - q->num_buffers += allocated_buffers;
>>
>> if (ret < 0) {
>> /*
>> @@ -2549,7 +2571,9 @@ void vb2_core_queue_release(struct vb2_queue *q)
>> __vb2_queue_free(q, q->max_num_buffers);
>> kfree(q->bufs);
>> q->bufs = NULL;
>> - q->num_buffers = 0;
>> + bitmap_free(q->bufs_bitmap);
>> + q->bufs_bitmap = NULL;
>> +
>> mutex_unlock(&q->mmap_lock);
>> }
>> EXPORT_SYMBOL_GPL(vb2_core_queue_release);
>> @@ -2904,7 +2928,7 @@ static size_t __vb2_perform_fileio(struct vb2_queue *q, char __user *data, size_
>> * Check if we need to dequeue the buffer.
>> */
>> index = fileio->cur_index;
>> - if (index >= q->num_buffers) {
>> + if (!test_bit(index, q->bufs_bitmap)) {
> I don't like this low level manipulation of queue internals here (after all
> the work other patches did to use helpers). Why not just keep
> vb2_get_num_buffers() here?

I will change that and put it in patch 8

>
>> struct vb2_buffer *b;
>>
>> /*
>> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
>> index 6986ff4b77cd..288477075a0e 100644
>> --- a/include/media/videobuf2-core.h
>> +++ b/include/media/videobuf2-core.h
>> @@ -346,7 +346,7 @@ struct vb2_buffer {
>> * describes the requested number of planes and sizes\[\]
>> * contains the requested plane sizes. In this case
>> * \*num_buffers are being allocated additionally to
>> - * q->num_buffers. If either \*num_planes or the requested
>> + * queue buffers. If either \*num_planes or the requested
> Perhaps "the buffers already in the queue"?

ok

>
>> * sizes are invalid callback must return %-EINVAL.
>> * @wait_prepare: release any locks taken while calling vb2 functions;
>> * it is called before an ioctl needs to wait for a new
>> @@ -557,7 +557,7 @@ struct vb2_buf_ops {
>> * @memory: current memory type used
>> * @dma_dir: DMA mapping direction.
>> * @bufs: videobuf2 buffer structures
>> - * @num_buffers: number of allocated/used buffers
>> + * @bufs_bitmap: bitmap to manage bufs entries.
> Perhaps "bitmap tracking whether each bufs[] entry is used"?

ok

>
>> * @max_num_buffers: upper limit of number of allocated/used buffers
>> * @queued_list: list of buffers currently queued from userspace
>> * @queued_count: number of buffers queued and ready for streaming.
>> @@ -621,7 +621,7 @@ struct vb2_queue {
>> unsigned int memory;
>> enum dma_data_direction dma_dir;
>> struct vb2_buffer **bufs;
>> - unsigned int num_buffers;
>> + unsigned long *bufs_bitmap;
>> unsigned int max_num_buffers;
>>
>> struct list_head queued_list;
>> @@ -1150,7 +1150,10 @@ static inline bool vb2_fileio_is_active(struct vb2_queue *q)
>> */
>> static inline unsigned int vb2_get_num_buffers(struct vb2_queue *q)
>> {
>> - return q->num_buffers;
>> + if (!q->bufs_bitmap)
>> + return 0;
>> +
>> + return bitmap_weight(q->bufs_bitmap, q->max_num_buffers);
> Hmm, could we just cache the number of buffers we have, so that we don't
> have to go over the entire bitmap every time? (Basically just keep the
> code that we had for handling q->num_buffers before this patch.)

I would prefer no duplicate how the number of buffers in a queue is computed
and bitmap offer helpers for that. Why not use it ?

>
>> }
>>
>> /**
>> @@ -1253,13 +1256,13 @@ static inline void vb2_clear_last_buffer_dequeued(struct vb2_queue *q)
>> static inline struct vb2_buffer *vb2_get_buffer(struct vb2_queue *q,
>> unsigned int index)
>> {
>> - if (!q->bufs)
>> + if (!q->bufs_bitmap)
>> return NULL;
>>
>> if (index >= q->max_num_buffers)
>> return NULL;
>>
>> - if (index < q->num_buffers)
>> + if (test_bit(index, q->bufs_bitmap))
> Aha, I see why we need the extra condition above now. Perhaps it should've
> been added in this patch instead?

For me it was more explicit do introduce it at the same time that
max_num_buffers field.

Regards,
Benjamin

>
>> return q->bufs[index];
>> return NULL;
>> }
>> --
>> 2.39.2
>>
> Best regards,
> Tomasz