Re: [PATCH for-next 0/4] singly linked list for chains

[Pavel Begunkov <asml.silence@gmail.com>]

On 15/10/2020 22:11, Pavel Begunkov wrote:
> see [3/4] and [4/4] for motivation, the other two are just preps.
> I wasn't expecting to find performance difference, but my naive nop
> test yeilds 5030 vs 5160 KIOPS, before and after [3/4] correspondingly.

Forgot to add that I want to review it thoroughly on silly bugs,
so until then it's more of RFC. 

> The test is submitting 32 linked nops and waits for them to complete.
> The testing is tuned for consistentcy, and the results are consistent
> across reboots.

The test was basically like the diff below.


diff --git a/tools/io_uring/io_uring-bench.c b/tools/io_uring/io_uring-bench.c
index 7703f0118385..84c4487c4d4e 100644
--- a/tools/io_uring/io_uring-bench.c
+++ b/tools/io_uring/io_uring-bench.c
@@ -96,13 +96,13 @@ static volatile int finish;
 /*
  * OPTIONS: Set these to test the various features of io_uring.
  */
-static int polled = 1;		/* use IO polling */
+static int polled = 0;		/* use IO polling */
 static int fixedbufs = 1;	/* use fixed user buffers */
 static int register_files = 1;	/* use fixed files */
 static int buffered = 0;	/* use buffered IO, not O_DIRECT */
 static int sq_thread_poll = 0;	/* use kernel submission/poller thread */
 static int sq_thread_cpu = -1;	/* pin above thread to this CPU */
-static int do_nop = 0;		/* no-op SQ ring commands */
+static int do_nop = 1;		/* no-op SQ ring commands */
 
 static int io_uring_register_buffers(struct submitter *s)
 {
@@ -149,6 +149,7 @@ static void init_io(struct submitter *s, unsigned index)
 
 	if (do_nop) {
 		sqe->opcode = IORING_OP_NOP;
+		sqe->flags = IOSQE_IO_LINK;
 		return;
 	}
 
-- 
Pavel Begunkov