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From: "Carter Li 李通洲" <carter.li@eoitek.com>
To: io-uring <io-uring@vger.kernel.org>
Subject: [ISSUE] The time cost of IOSQE_IO_LINK
Date: Wed, 12 Feb 2020 16:31:31 +0000
Message-ID: <9FEF0D34-A012-4505-AA4E-FF97CC302A33@eoitek.com> (raw)

Hi everyone,

IOSQE_IO_LINK seems to have very high cost, even greater then io_uring_enter syscall.

Test code attached below. The program completes after getting 100000000 cqes.

$ gcc test.c -luring -o test0 -g -O3 -DUSE_LINK=0
$ time ./test0
USE_LINK: 0, count: 100000000, submit_count: 1562500
0.99user 9.99system 0:11.02elapsed 99%CPU (0avgtext+0avgdata 1608maxresident)k
0inputs+0outputs (0major+72minor)pagefaults 0swaps

$ gcc test.c -luring -o test1 -g -O3 -DUSE_LINK=1
$ time ./test1
USE_LINK: 1, count: 100000110, submit_count: 799584
0.83user 19.21system 0:20.90elapsed 95%CPU (0avgtext+0avgdata 1632maxresident)k
0inputs+0outputs (0major+72minor)pagefaults 0swaps

As you can see, the `-DUSE_LINK=1` version emits only about half io_uring_submit calls
of the other version, but takes twice as long. That makes IOSQE_IO_LINK almost useless,
please have a check.

Thanks,
Carter Li

---

#include <liburing.h>
#include <stdio.h>

#define ENTRY_SIZE 128
#define MAX_COUNT 100000000

#ifndef USE_LINK
#	define USE_LINK 0
#endif

int main(void) {
	struct io_uring ring;
	unsigned i, head;
	unsigned count = 0, cqe_count = 0, submit_count = 0;
	struct io_uring_sqe *sqe;
	struct io_uring_cqe *cqe;

	if (io_uring_queue_init(ENTRY_SIZE, &ring, 0) < 0) {
		return -1;
	}

	for (i = 0; i < ENTRY_SIZE / 2; ++i) {
		sqe = io_uring_get_sqe(&ring);
		io_uring_prep_nop(sqe);
#if USE_LINK
		io_uring_sqe_set_flags(sqe, IOSQE_IO_LINK);
		sqe = io_uring_get_sqe(&ring);
		io_uring_prep_nop(sqe);
		sqe->user_data = 1;
#endif
	}

	while (count < MAX_COUNT) {
		io_uring_submit_and_wait(&ring, 1);
		++submit_count;

		io_uring_for_each_cqe(&ring, head, cqe) {
			++cqe_count;
			++count;
#if USE_LINK
			if (cqe->user_data) {
				sqe = io_uring_get_sqe(&ring);
				io_uring_prep_nop(sqe);
				io_uring_sqe_set_flags(sqe, IOSQE_IO_LINK);
				sqe = io_uring_get_sqe(&ring);
				io_uring_prep_nop(sqe);
				sqe->user_data = 1;
			}
#else
			sqe = io_uring_get_sqe(&ring);
			io_uring_prep_nop(sqe);
			sqe->user_data = !cqe->user_data;
#endif
		}
		io_uring_cq_advance(&ring, cqe_count);
		cqe_count = 0;
	}

	printf("USE_LINK: %d, count: %u, submit_count: %u\n\n",
		USE_LINK, count, submit_count);
}



             reply index

Thread overview: 59+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-12 16:31 Carter Li 李通洲 [this message]
2020-02-12 17:11 ` Jens Axboe
2020-02-12 17:22   ` Jens Axboe
2020-02-12 17:29     ` Jens Axboe
2020-02-13  0:33   ` Carter Li 李通洲
2020-02-13 15:08     ` Pavel Begunkov
2020-02-13 15:14       ` Jens Axboe
2020-02-13 15:51         ` Carter Li 李通洲
2020-02-14  1:25           ` Carter Li 李通洲
2020-02-14  2:45             ` Jens Axboe
2020-02-14  5:03               ` Jens Axboe
2020-02-14 15:32                 ` Peter Zijlstra
2020-02-14 15:47                   ` Jens Axboe
2020-02-14 16:18                     ` Jens Axboe
2020-02-14 17:52                       ` Jens Axboe
2020-02-14 20:44                         ` Jens Axboe
2020-02-15  0:16                           ` Carter Li 李通洲
2020-02-15  1:10                             ` Jens Axboe
2020-02-15  1:25                               ` Carter Li 李通洲
2020-02-15  1:27                                 ` Jens Axboe
2020-02-15  6:01                                   ` Jens Axboe
2020-02-15  6:32                                     ` Carter Li 李通洲
2020-02-15 15:11                                       ` Jens Axboe
2020-02-16 19:06                                     ` Pavel Begunkov
2020-02-16 22:23                                       ` Jens Axboe
2020-02-17 10:30                                         ` Pavel Begunkov
2020-02-17 19:30                                           ` Jens Axboe
2020-02-16 23:06                                       ` Jens Axboe
2020-02-16 23:07                                         ` Jens Axboe
2020-02-17 12:09                           ` Peter Zijlstra
2020-02-17 16:12                             ` Jens Axboe
2020-02-17 17:16                               ` Jens Axboe
2020-02-17 17:46                                 ` Peter Zijlstra
2020-02-17 18:16                                   ` Jens Axboe
2020-02-18 13:13                                     ` Peter Zijlstra
2020-02-18 14:27                                       ` [PATCH] asm-generic/atomic: Add try_cmpxchg() fallbacks Peter Zijlstra
2020-02-18 14:40                                         ` Peter Zijlstra
2020-02-20 10:30                                         ` Will Deacon
2020-02-20 10:37                                           ` Peter Zijlstra
2020-02-20 10:39                                             ` Will Deacon
2020-02-18 14:56                                       ` [ISSUE] The time cost of IOSQE_IO_LINK Oleg Nesterov
2020-02-18 15:07                                         ` Oleg Nesterov
2020-02-18 15:38                                           ` Peter Zijlstra
2020-02-18 16:33                                             ` Jens Axboe
2020-02-18 15:07                                         ` Peter Zijlstra
2020-02-18 15:50                                           ` [PATCH] task_work_run: don't take ->pi_lock unconditionally Oleg Nesterov
2020-02-20 16:39                                             ` Peter Zijlstra
2020-02-20 17:22                                               ` Oleg Nesterov
2020-02-20 17:49                                                 ` Peter Zijlstra
2020-02-21 14:52                                                   ` Oleg Nesterov
2020-02-24 18:47                                                     ` Jens Axboe
2020-02-28 19:17                                                       ` Jens Axboe
2020-02-28 19:25                                                         ` Peter Zijlstra
2020-02-28 19:28                                                           ` Jens Axboe
2020-02-28 20:06                                                             ` Peter Zijlstra
2020-02-28 20:15                                                               ` Jens Axboe
2020-02-18 16:46                                       ` [ISSUE] The time cost of IOSQE_IO_LINK Jens Axboe
2020-02-18 16:52                                         ` Jens Axboe
2020-02-18 13:13                               ` Peter Zijlstra

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