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Message-ID: <8f683397-f0e2-4701-9a4b-5b5c32d25915@collabora.com>
Date: Mon, 15 Jan 2024 15:51:41 +0100
From: Benjamin Gaignard <benjamin.gaignard@...labora.com>
To: Hans Verkuil <hverkuil@...all.nl>, mchehab@...nel.org
Cc: linux-kernel@...r.kernel.org, linux-media@...r.kernel.org,
kernel@...labora.com
Subject: Re: [PATCH v16 4/8] media: core: Add bitmap manage bufs array entries
Le 15/01/2024 à 13:21, Hans Verkuil a écrit :
> On 15/12/2023 10:08, 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@...labora.com>
>> ---
>> .../media/common/videobuf2/videobuf2-core.c | 37 ++++++++++++++++---
>> include/media/videobuf2-core.h | 17 +++++----
>> 2 files changed, 41 insertions(+), 13 deletions(-)
>>
>> diff --git a/drivers/media/common/videobuf2/videobuf2-core.c b/drivers/media/common/videobuf2/videobuf2-core.c
>> index cd2b9e51b9b0..9509535a980c 100644
>> --- a/drivers/media/common/videobuf2/videobuf2-core.c
>> +++ b/drivers/media/common/videobuf2/videobuf2-core.c
>> @@ -421,11 +421,12 @@ 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] || vb->vb2_queue);
>> + WARN_ON(index >= q->max_num_buffers || test_bit(index, q->bufs_bitmap) || vb->vb2_queue);
>>
>> q->bufs[index] = vb;
>> vb->index = index;
>> vb->vb2_queue = q;
>> + set_bit(index, q->bufs_bitmap);
>> }
>>
>> /**
>> @@ -434,6 +435,7 @@ 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;
>> }
>> @@ -462,7 +464,8 @@ static int __vb2_queue_alloc(struct vb2_queue *q, enum vb2_memory memory,
>> 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);
> Shouldn't this check if this call fails to find an area of 'num_buffers' 0-bits?
> Or, alternatively, keep reducing num_buffers until it finds a free range. I'm
> not sure what is best.
I will add a check on the return value. If it can't allocate the requested number of buffers
it will fail. Userspace can decide if it wants to try allocated less buffers or not.
>>
>> *first_index = index;
>>
>> @@ -664,7 +667,6 @@ 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);
>> @@ -882,6 +884,14 @@ 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)
>> @@ -951,7 +961,6 @@ 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) {
>> /*
>> @@ -978,6 +987,10 @@ 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);
>> @@ -1014,9 +1027,19 @@ 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);
>> + if (!q->bufs_bitmap) {
>> + ret = -ENOMEM;
>> + kfree(q->bufs);
>> + q->bufs = NULL;
>> + }
> The same code is used in reqbufs and create_bufs, so perhaps creating a helper
> function is better.
I will add vb2_core_allocated_queue_buffers_storage() and vb2_core_free_queue_buffers_storage().
>
>> mutex_unlock(&q->mmap_lock);
>> +unlock:
>> if (ret)
>> return ret;
>> q->waiting_for_buffers = !q->is_output;
>> @@ -1078,7 +1101,6 @@ 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) {
>> /*
>> @@ -2567,6 +2589,9 @@ void vb2_core_queue_release(struct vb2_queue *q)
>> __vb2_queue_free(q, vb2_get_num_buffers(q));
>> kfree(q->bufs);
>> q->bufs = NULL;
>> + bitmap_free(q->bufs_bitmap);
>> + q->bufs_bitmap = NULL;
>> +
> And perhaps also a helper function to free the memory.
>
>> mutex_unlock(&q->mmap_lock);
>> }
>> EXPORT_SYMBOL_GPL(vb2_core_queue_release);
>> diff --git a/include/media/videobuf2-core.h b/include/media/videobuf2-core.h
>> index 607f2ba7a905..e4c1fc7ae82f 100644
>> --- a/include/media/videobuf2-core.h
>> +++ b/include/media/videobuf2-core.h
>> @@ -346,8 +346,8 @@ 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
>> - * sizes are invalid callback must return %-EINVAL.
>> + * the buffers already in the queue. If either \*num_planes
> already in the queue -> already allocated
>
>> + * or the requested 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
>> * buffer to arrive; required to avoid a deadlock in
>> @@ -572,7 +572,7 @@ 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 tracking whether each bufs[] entry is used
>> * @max_num_buffers: upper limit of number of allocated/used buffers.
>> * If set to 0 v4l2 core will change it VB2_MAX_FRAME
>> * for backward compatibility.
>> @@ -639,7 +639,7 @@ 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;
>> @@ -1168,7 +1168,10 @@ 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);
> I'd invert the test:
>
> if (q->bufs_bitmap)
> return bitmap_weight(q->bufs_bitmap, q->max_num_buffers);
> return 0;
>
> It's a little bit easier to read.
>
>> }
>>
>> /**
>> @@ -1271,13 +1274,13 @@ 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)
> Can you ever have q->bufs set, but not q->bufs_bitmap?
>
> I think the original check is just fine.
>
> It is probably a good idea to perhaps clarify this in the @bufs documentation:
> if it is non-NULL, then bufs_bitmap is also non-NULL.
>
> And ensure that where you allocate and assign these fields that bufs_bitmap
> is always non-NULL when assigning q->bufs. Then it is enough to just test
> q->bufs to be certain both bufs and bufs_bitmap are non-NULL.
I will add that in the documentation.
>
>> return NULL;
>>
>> if (index >= q->max_num_buffers)
>> return NULL;
>>
>> - if (index < q->num_buffers)
>> + if (test_bit(index, q->bufs_bitmap))
>> return q->bufs[index];
>> return NULL;
>> }
> Adding support for deleting buffers also causes a odd change in behavior
> of CREATE_BUFS w.r.t. the index field of struct v4l2_create_buffers:
> when adding new buffers, the index field is indeed the starting buffer index,
> as per the documentation. But if count == 0, then the index field returns
> the total number of allocated buffers, which is really something different.
>
> I think the documentation of VIDIOC_CREATE_BUFS should be updated to clearly
> state that if count == 0, then 'index' is set to the total number of
> allocated buffers.
>
> I really hate VIDIOC_CREATE_BUFS, and I do plan an RFC with a proposal for
> an alternative API.
>
> Regards,
>
> Hans
>
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