Re: [PATCH 11/11] io_uring: get rid of intermediate aux cqe caches

[Jens Axboe <axboe@kernel.dk>]

On 3/15/24 10:25 AM, Jens Axboe wrote:
> On 3/15/24 10:23 AM, Pavel Begunkov wrote:
>> On 3/15/24 16:20, Jens Axboe wrote:
>>> On 3/15/24 9:30 AM, Pavel Begunkov wrote:
>>>> io_post_aux_cqe(), which is used for multishot requests, delays
>>>> completions by putting CQEs into a temporary array for the purpose
>>>> completion lock/flush batching.
>>>>
>>>> DEFER_TASKRUN doesn't need any locking, so for it we can put completions
>>>> directly into the CQ and defer post completion handling with a flag.
>>>> That leaves !DEFER_TASKRUN, which is not that interesting / hot for
>>>> multishot requests, so have conditional locking with deferred flush
>>>> for them.
>>>
>>> This breaks the read-mshot test case, looking into what is going on
>>> there.
>>
>> I forgot to mention, yes it does, the test makes odd assumptions about
>> overflows, IIRC it expects that the kernel allows one and only one aux
>> CQE to be overflown. Let me double check
> 
> Yeah this is very possible, the overflow checking could be broken in
> there. I'll poke at it and report back.

It does, this should fix it:


diff --git a/test/read-mshot.c b/test/read-mshot.c
index 8fcb79857bf0..501ca69a98dc 100644
--- a/test/read-mshot.c
+++ b/test/read-mshot.c
@@ -236,7 +236,7 @@ static int test(int first_good, int async, int overflow)
 		}
 		if (!(cqe->flags & IORING_CQE_F_MORE)) {
 			/* we expect this on overflow */
-			if (overflow && (i - 1 == NR_OVERFLOW))
+			if (overflow && i >= NR_OVERFLOW)
 				break;
 			fprintf(stderr, "no more cqes\n");
 			return 1;

-- 
Jens Axboe