On 7/7/20 11:29 PM, Xiaoguang Wang wrote:
> I modify above test program a bit:
> #include <errno.h>
> #include <stdio.h>
> #include <unistd.h>
> #include <stdlib.h>
> #include <string.h>
> #include <fcntl.h>
> #include <assert.h>
>
> #include "liburing.h"
>
> static void test_cq_overflow(struct io_uring *ring)
> {
> struct io_uring_cqe *cqe;
> struct io_uring_sqe *sqe;
> int issued = 0;
> int ret = 0;
> int i;
>
> for (i = 0; i < 33; i++) {
> sqe = io_uring_get_sqe(ring);
> if (!sqe) {
> fprintf(stderr, "get sqe failed\n");
> break;;
> }
> ret = io_uring_submit(ring);
> if (ret <= 0) {
> if (ret != -EBUSY)
> fprintf(stderr, "sqe submit failed: %d\n", ret);
> break;
> }
> issued++;
> }
>
> printf("issued requests: %d\n", issued);
>
> while (issued) {
> ret = io_uring_peek_cqe(ring, &cqe);
> if (ret) {
> if (ret != -EAGAIN) {
> fprintf(stderr, "peek completion failed: %s\n",
> strerror(ret));
> break;
> }
> printf("left requets: %d %d\n", issued, IO_URING_READ_ONCE(*ring->sq.kflags));
> continue;
> }
> io_uring_cqe_seen(ring, cqe);
> issued--;
> printf("left requets: %d\n", issued);
> }
> }
>
> int main(int argc, char *argv[])
> {
> int ret;
> struct io_uring ring;
>
> ret = io_uring_queue_init(16, &ring, 0);
> if (ret) {
> fprintf(stderr, "ring setup failed: %d\n", ret);
> return 1;
> }
>
> test_cq_overflow(&ring);
> return 0;
> }
>
> Though with your patches applied, we still can not peek the last cqe.
> This test program will only issue 33 sqes, so it won't get EBUSY error.
How about we make this even simpler, then - make the
IORING_SQ_CQ_OVERFLOW actually track the state, rather than when we fail
on submission. The liburing change would be the same, the kernel side
would then look like the below.
diff --git a/fs/io_uring.c b/fs/io_uring.c
index 4c9a494c9f9f..01981926cdf4 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1342,6 +1342,7 @@ static bool io_cqring_overflow_flush(struct io_ring_ctx *ctx, bool force)
if (cqe) {
clear_bit(0, &ctx->sq_check_overflow);
clear_bit(0, &ctx->cq_check_overflow);
+ ctx->rings->sq_flags &= ~IORING_SQ_CQ_OVERFLOW;
}
spin_unlock_irqrestore(&ctx->completion_lock, flags);
io_cqring_ev_posted(ctx);
@@ -1379,6 +1380,7 @@ static void __io_cqring_fill_event(struct io_kiocb *req, long res, long cflags)
if (list_empty(&ctx->cq_overflow_list)) {
set_bit(0, &ctx->sq_check_overflow);
set_bit(0, &ctx->cq_check_overflow);
+ ctx->rings->sq_flags |= IORING_SQ_CQ_OVERFLOW;
}
req->flags |= REQ_F_OVERFLOW;
refcount_inc(&req->refs);
@@ -6375,9 +6377,9 @@ static int io_sq_thread(void *data)
}
/* Tell userspace we may need a wakeup call */
+ spin_lock_irq(&ctx->completion_lock);
ctx->rings->sq_flags |= IORING_SQ_NEED_WAKEUP;
- /* make sure to read SQ tail after writing flags */
- smp_mb();
+ spin_unlock_irq(&ctx->completion_lock);
to_submit = io_sqring_entries(ctx);
if (!to_submit || ret == -EBUSY) {
@@ -6400,7 +6402,9 @@ static int io_sq_thread(void *data)
}
finish_wait(&ctx->sqo_wait, &wait);
+ spin_lock_irq(&ctx->completion_lock);
ctx->rings->sq_flags &= ~IORING_SQ_NEED_WAKEUP;
+ spin_unlock_irq(&ctx->completion_lock);
}
mutex_lock(&ctx->uring_lock);
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 8d033961cb78..91953b543125 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -198,6 +198,7 @@ struct io_sqring_offsets {
* sq_ring->flags
*/
#define IORING_SQ_NEED_WAKEUP (1U << 0) /* needs io_uring_enter wakeup */
+#define IORING_SQ_CQ_OVERFLOW (1U << 1) /* app needs to enter kernel */
struct io_cqring_offsets {
__u32 head;
--
Jens Axboe
