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authorJens Axboe <axboe@kernel.dk>2022-03-08 17:46:52 -0700
committerJens Axboe <axboe@kernel.dk>2022-03-10 06:33:14 -0700
commitcc3cec8367cba76a8ae4c271eba8450f3efc1ba3 (patch)
tree23a60579ae1cc6438208a64d7be4867f5240de9f
parente7a6c00dc77aedf27a601738ea509f1caea6d673 (diff)
io_uring: speedup provided buffer handling
In testing high frequency workloads with provided buffers, we spend a lot of time in allocating and freeing the buffer units themselves. Rather than repeatedly free and alloc them, add a recycling cache instead. There are two caches: - ctx->io_buffers_cache. This is the one we grab from in the submission path, and it's protected by ctx->uring_lock. For inline completions, we can recycle straight back to this cache and not need any extra locking. - ctx->io_buffers_comp. If we're not under uring_lock, then we use this list to recycle buffers. It's protected by the completion_lock. On adding a new buffer, check io_buffers_cache. If it's empty, check if we can splice entries from the io_buffers_comp_cache. This reduces about 5-10% of overhead from provided buffers, bringing it pretty close to the non-provided path. Signed-off-by: Jens Axboe <axboe@kernel.dk>
-rw-r--r--fs/io_uring.c139
1 files changed, 117 insertions, 22 deletions
diff --git a/fs/io_uring.c b/fs/io_uring.c
index daa3609b742f..0f5e999e569f 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -384,6 +384,7 @@ struct io_ring_ctx {
struct list_head ltimeout_list;
struct list_head cq_overflow_list;
struct xarray io_buffers;
+ struct list_head io_buffers_cache;
struct xarray personalities;
u32 pers_next;
unsigned sq_thread_idle;
@@ -426,6 +427,8 @@ struct io_ring_ctx {
struct hlist_head *cancel_hash;
unsigned cancel_hash_bits;
bool poll_multi_queue;
+
+ struct list_head io_buffers_comp;
} ____cacheline_aligned_in_smp;
struct io_restriction restrictions;
@@ -441,6 +444,8 @@ struct io_ring_ctx {
struct llist_head rsrc_put_llist;
struct list_head rsrc_ref_list;
spinlock_t rsrc_ref_lock;
+
+ struct list_head io_buffers_pages;
};
/* Keep this last, we don't need it for the fast path */
@@ -1278,24 +1283,56 @@ static inline void io_req_set_rsrc_node(struct io_kiocb *req,
}
}
-static unsigned int __io_put_kbuf(struct io_kiocb *req)
+static unsigned int __io_put_kbuf(struct io_kiocb *req, struct list_head *list)
{
struct io_buffer *kbuf = req->kbuf;
unsigned int cflags;
- cflags = kbuf->bid << IORING_CQE_BUFFER_SHIFT;
- cflags |= IORING_CQE_F_BUFFER;
+ cflags = IORING_CQE_F_BUFFER | (kbuf->bid << IORING_CQE_BUFFER_SHIFT);
req->flags &= ~REQ_F_BUFFER_SELECTED;
- kfree(kbuf);
+ list_add(&kbuf->list, list);
req->kbuf = NULL;
return cflags;
}
-static inline unsigned int io_put_kbuf(struct io_kiocb *req)
+static inline unsigned int io_put_kbuf_comp(struct io_kiocb *req)
{
if (likely(!(req->flags & REQ_F_BUFFER_SELECTED)))
return 0;
- return __io_put_kbuf(req);
+ return __io_put_kbuf(req, &req->ctx->io_buffers_comp);
+}
+
+static inline unsigned int io_put_kbuf(struct io_kiocb *req,
+ unsigned issue_flags)
+{
+ unsigned int cflags;
+
+ if (likely(!(req->flags & REQ_F_BUFFER_SELECTED)))
+ return 0;
+
+ /*
+ * We can add this buffer back to two lists:
+ *
+ * 1) The io_buffers_cache list. This one is protected by the
+ * ctx->uring_lock. If we already hold this lock, add back to this
+ * list as we can grab it from issue as well.
+ * 2) The io_buffers_comp list. This one is protected by the
+ * ctx->completion_lock.
+ *
+ * We migrate buffers from the comp_list to the issue cache list
+ * when we need one.
+ */
+ if (issue_flags & IO_URING_F_UNLOCKED) {
+ struct io_ring_ctx *ctx = req->ctx;
+
+ spin_lock(&ctx->completion_lock);
+ cflags = __io_put_kbuf(req, &ctx->io_buffers_comp);
+ spin_unlock(&ctx->completion_lock);
+ } else {
+ cflags = __io_put_kbuf(req, &req->ctx->io_buffers_cache);
+ }
+
+ return cflags;
}
static bool io_match_task(struct io_kiocb *head, struct task_struct *task,
@@ -1443,6 +1480,7 @@ static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
init_waitqueue_head(&ctx->sqo_sq_wait);
INIT_LIST_HEAD(&ctx->sqd_list);
INIT_LIST_HEAD(&ctx->cq_overflow_list);
+ INIT_LIST_HEAD(&ctx->io_buffers_cache);
init_completion(&ctx->ref_comp);
xa_init_flags(&ctx->io_buffers, XA_FLAGS_ALLOC1);
xa_init_flags(&ctx->personalities, XA_FLAGS_ALLOC1);
@@ -1451,6 +1489,8 @@ static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
spin_lock_init(&ctx->completion_lock);
spin_lock_init(&ctx->timeout_lock);
INIT_WQ_LIST(&ctx->iopoll_list);
+ INIT_LIST_HEAD(&ctx->io_buffers_pages);
+ INIT_LIST_HEAD(&ctx->io_buffers_comp);
INIT_LIST_HEAD(&ctx->defer_list);
INIT_LIST_HEAD(&ctx->timeout_list);
INIT_LIST_HEAD(&ctx->ltimeout_list);
@@ -2329,7 +2369,8 @@ static void handle_prev_tw_list(struct io_wq_work_node *node,
if (likely(*uring_locked))
req->io_task_work.func(req, uring_locked);
else
- __io_req_complete_post(req, req->result, io_put_kbuf(req));
+ __io_req_complete_post(req, req->result,
+ io_put_kbuf_comp(req));
node = next;
} while (node);
@@ -2679,7 +2720,7 @@ static int io_do_iopoll(struct io_ring_ctx *ctx, bool force_nonspin)
if (unlikely(req->flags & REQ_F_CQE_SKIP))
continue;
- __io_fill_cqe(req, req->result, io_put_kbuf(req));
+ __io_fill_cqe(req, req->result, io_put_kbuf(req, 0));
nr_events++;
}
@@ -2855,14 +2896,14 @@ static bool __io_complete_rw_common(struct io_kiocb *req, long res)
static inline void io_req_task_complete(struct io_kiocb *req, bool *locked)
{
- unsigned int cflags = io_put_kbuf(req);
int res = req->result;
if (*locked) {
- io_req_complete_state(req, res, cflags);
+ io_req_complete_state(req, res, io_put_kbuf(req, 0));
io_req_add_compl_list(req);
} else {
- io_req_complete_post(req, res, cflags);
+ io_req_complete_post(req, res,
+ io_put_kbuf(req, IO_URING_F_UNLOCKED));
}
}
@@ -2871,7 +2912,8 @@ static void __io_complete_rw(struct io_kiocb *req, long res,
{
if (__io_complete_rw_common(req, res))
return;
- __io_req_complete(req, issue_flags, req->result, io_put_kbuf(req));
+ __io_req_complete(req, issue_flags, req->result,
+ io_put_kbuf(req, issue_flags));
}
static void io_complete_rw(struct kiocb *kiocb, long res)
@@ -4518,13 +4560,11 @@ static int __io_remove_buffers(struct io_ring_ctx *ctx, struct io_buffer *buf,
nxt = list_first_entry(&buf->list, struct io_buffer, list);
list_del(&nxt->list);
- kfree(nxt);
if (++i == nbufs)
return i;
cond_resched();
}
i++;
- kfree(buf);
xa_erase(&ctx->io_buffers, bgid);
return i;
@@ -4590,17 +4630,63 @@ static int io_provide_buffers_prep(struct io_kiocb *req,
return 0;
}
-static int io_add_buffers(struct io_provide_buf *pbuf, struct io_buffer **head)
+static int io_refill_buffer_cache(struct io_ring_ctx *ctx)
+{
+ struct io_buffer *buf;
+ struct page *page;
+ int bufs_in_page;
+
+ /*
+ * Completions that don't happen inline (eg not under uring_lock) will
+ * add to ->io_buffers_comp. If we don't have any free buffers, check
+ * the completion list and splice those entries first.
+ */
+ if (!list_empty_careful(&ctx->io_buffers_comp)) {
+ spin_lock(&ctx->completion_lock);
+ if (!list_empty(&ctx->io_buffers_comp)) {
+ list_splice_init(&ctx->io_buffers_comp,
+ &ctx->io_buffers_cache);
+ spin_unlock(&ctx->completion_lock);
+ return 0;
+ }
+ spin_unlock(&ctx->completion_lock);
+ }
+
+ /*
+ * No free buffers and no completion entries either. Allocate a new
+ * page worth of buffer entries and add those to our freelist.
+ */
+ page = alloc_page(GFP_KERNEL_ACCOUNT);
+ if (!page)
+ return -ENOMEM;
+
+ list_add(&page->lru, &ctx->io_buffers_pages);
+
+ buf = page_address(page);
+ bufs_in_page = PAGE_SIZE / sizeof(*buf);
+ while (bufs_in_page) {
+ list_add_tail(&buf->list, &ctx->io_buffers_cache);
+ buf++;
+ bufs_in_page--;
+ }
+
+ return 0;
+}
+
+static int io_add_buffers(struct io_ring_ctx *ctx, struct io_provide_buf *pbuf,
+ struct io_buffer **head)
{
struct io_buffer *buf;
u64 addr = pbuf->addr;
int i, bid = pbuf->bid;
for (i = 0; i < pbuf->nbufs; i++) {
- buf = kmalloc(sizeof(*buf), GFP_KERNEL_ACCOUNT);
- if (!buf)
+ if (list_empty(&ctx->io_buffers_cache) &&
+ io_refill_buffer_cache(ctx))
break;
-
+ buf = list_first_entry(&ctx->io_buffers_cache, struct io_buffer,
+ list);
+ list_del(&buf->list);
buf->addr = addr;
buf->len = min_t(__u32, pbuf->len, MAX_RW_COUNT);
buf->bid = bid;
@@ -4632,7 +4718,7 @@ static int io_provide_buffers(struct io_kiocb *req, unsigned int issue_flags)
list = head = xa_load(&ctx->io_buffers, p->bgid);
- ret = io_add_buffers(p, &head);
+ ret = io_add_buffers(ctx, p, &head);
if (ret >= 0 && !list) {
ret = xa_insert(&ctx->io_buffers, p->bgid, head, GFP_KERNEL);
if (ret < 0)
@@ -5229,7 +5315,7 @@ static int io_recvmsg(struct io_kiocb *req, unsigned int issue_flags)
if (kmsg->free_iov)
kfree(kmsg->free_iov);
req->flags &= ~REQ_F_NEED_CLEANUP;
- __io_req_complete(req, issue_flags, ret, io_put_kbuf(req));
+ __io_req_complete(req, issue_flags, ret, io_put_kbuf(req, issue_flags));
return 0;
}
@@ -5284,7 +5370,8 @@ static int io_recv(struct io_kiocb *req, unsigned int issue_flags)
out_free:
req_set_fail(req);
}
- __io_req_complete(req, issue_flags, ret, io_put_kbuf(req));
+
+ __io_req_complete(req, issue_flags, ret, io_put_kbuf(req, issue_flags));
return 0;
}
@@ -6704,7 +6791,7 @@ fail:
static void io_clean_op(struct io_kiocb *req)
{
if (req->flags & REQ_F_BUFFER_SELECTED)
- io_put_kbuf(req);
+ io_put_kbuf_comp(req);
if (req->flags & REQ_F_NEED_CLEANUP) {
switch (req->opcode) {
@@ -9475,6 +9562,14 @@ static void io_destroy_buffers(struct io_ring_ctx *ctx)
xa_for_each(&ctx->io_buffers, index, buf)
__io_remove_buffers(ctx, buf, index, -1U);
+
+ while (!list_empty(&ctx->io_buffers_pages)) {
+ struct page *page;
+
+ page = list_first_entry(&ctx->io_buffers_pages, struct page, lru);
+ list_del_init(&page->lru);
+ __free_page(page);
+ }
}
static void io_req_caches_free(struct io_ring_ctx *ctx)