Provided buffers allow an application to supply io_uring with buffers
that can then be grabbed for a read/receive request, when the data
source is ready to deliver data. The existing scheme relies on using
IORING_OP_PROVIDE_BUFFERS to do that, but it can be difficult to use
in real world applications. It's pretty efficient if the application
is able to supply back batches of provided buffers when they have been
consumed and the application is ready to recycle them, but if
fragmentation occurs in the buffer space, it can become difficult to
supply enough buffers at the time. This hurts efficiency.
Add a register op, IORING_REGISTER_PBUF_RING, which allows an application
to setup a shared queue for each buffer group of provided buffers. The
application can then supply buffers simply by adding them to this ring,
and the kernel can consume then just as easily. The ring shares the head
with the application, the tail remains private in the kernel.
Provided buffers setup with IORING_REGISTER_PBUF_RING cannot use
IORING_OP_{PROVIDE,REMOVE}_BUFFERS for adding or removing entries to the
ring, they must use the mapped ring. Mapped provided buffer rings can
co-exist with normal provided buffers, just not within the same group ID.
To gauge overhead of the existing scheme and evaluate the mapped ring
approach, a simple NOP benchmark was written. It uses a ring of 128
entries, and submits/completes 32 at the time. 'Replenish' is how
many buffers are provided back at the time after they have been
consumed:
Test Replenish NOPs/sec
================================================================
No provided buffers NA ~30M
Provided buffers 32 ~16M
Provided buffers 1 ~10M
Ring buffers 32 ~27M
Ring buffers 1 ~27M
The ring mapped buffers perform almost as well as not using provided
buffers at all, and they don't care if you provided 1 or more back at
the same time. This means application can just replenish as they go,
rather than need to batch and compact, further reducing overhead in the
application. The NOP benchmark above doesn't need to do any compaction,
so that overhead isn't even reflected in the above test.
Co-developed-by: Dylan Yudaken <dylany@xxxxxx>
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
---
fs/io_uring.c | 233 ++++++++++++++++++++++++++++++++--
include/uapi/linux/io_uring.h | 36 ++++++
2 files changed, 257 insertions(+), 12 deletions(-)
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 5867dcabc73b..776a9f5e5ec7 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -285,9 +285,26 @@ struct io_rsrc_data {
bool quiesce;
};
+#define IO_BUFFER_LIST_BUF_PER_PAGE (PAGE_SIZE / sizeof(struct io_uring_buf))
struct io_buffer_list {
- struct list_head buf_list;
+ /*
+ * If ->buf_nr_pages is set, then buf_pages/buf_ring are used. If not,
+ * then these are classic provided buffers and ->buf_list is used.
+ */
+ union {
+ struct list_head buf_list;
+ struct {
+ struct page **buf_pages;
+ struct io_uring_buf_ring *buf_ring;
+ };
+ };
__u16 bgid;
+
+ /* below is for ring provided buffers */
+ __u16 buf_nr_pages;
+ __u16 nr_entries;
+ __u32 tail;
+ __u32 mask;
};
struct io_buffer {
@@ -804,6 +821,7 @@ enum {
REQ_F_NEED_CLEANUP_BIT,
REQ_F_POLLED_BIT,
REQ_F_BUFFER_SELECTED_BIT,
+ REQ_F_BUFFER_RING_BIT,
REQ_F_COMPLETE_INLINE_BIT,
REQ_F_REISSUE_BIT,
REQ_F_CREDS_BIT,
@@ -855,6 +873,8 @@ enum {
REQ_F_POLLED = BIT(REQ_F_POLLED_BIT),
/* buffer already selected */
REQ_F_BUFFER_SELECTED = BIT(REQ_F_BUFFER_SELECTED_BIT),
+ /* buffer selected from ring, needs commit */
+ REQ_F_BUFFER_RING = BIT(REQ_F_BUFFER_RING_BIT),
/* completion is deferred through io_comp_state */
REQ_F_COMPLETE_INLINE = BIT(REQ_F_COMPLETE_INLINE_BIT),
/* caller should reissue async */
@@ -979,6 +999,12 @@ struct io_kiocb {
/* stores selected buf, valid IFF REQ_F_BUFFER_SELECTED is set */
struct io_buffer *kbuf;
+
+ /*
+ * stores buffer ID for ring provided buffers, valid IFF
+ * REQ_F_BUFFER_RING is set.
+ */
+ struct io_buffer_list *buf_list;
};
union {
@@ -1470,8 +1496,14 @@ static inline void io_req_set_rsrc_node(struct io_kiocb *req,
static unsigned int __io_put_kbuf(struct io_kiocb *req, struct list_head *list)
{
- req->flags &= ~REQ_F_BUFFER_SELECTED;
- list_add(&req->kbuf->list, list);
+ if (req->flags & REQ_F_BUFFER_RING) {
+ if (req->buf_list)
+ req->buf_list->tail++;
