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From: Jens Axboe <axboe@kernel.dk>
To: Jackie Liu <liuyun01@kylinos.cn>
Cc: yangerkun <yangerkun@huawei.com>, linux-block@vger.kernel.org
Subject: Re: [PATCH 1/2] io_uring: make the logic clearer for io_sequence_defer
Date: Thu, 10 Oct 2019 21:47:03 -0600
Message-ID: <617f81c3-4633-e1b2-f51b-ae63fb071237@kernel.dk> (raw)
In-Reply-To: <71C4794E-2B1F-4A29-93E9-D578E71DECED@kylinos.cn>

On 10/10/19 9:43 PM, Jackie Liu wrote:
> 
> 
>> 2019年10月11日 11:42,Jens Axboe <axboe@kernel.dk> 写道:
>>
>> On 10/10/19 9:41 PM, Jackie Liu wrote:
>>>
>>>
>>>> 2019年10月11日 11:34,Jens Axboe <axboe@kernel.dk> 写道:
>>>>
>>>> On 10/10/19 9:27 PM, Jackie Liu wrote:
>>>>>
>>>>>
>>>>>> 2019年10月11日 11:17,Jens Axboe <axboe@kernel.dk> 写道:
>>>>>>
>>>>>> On 10/10/19 9:06 PM, Jackie Liu wrote:
>>>>>>>
>>>>>>>
>>>>>>>> 2019年10月11日 10:35,Jens Axboe <axboe@kernel.dk> 写道:
>>>>>>>>
>>>>>>>> On 10/10/19 8:24 PM, yangerkun wrote:
>>>>>>>>>
>>>>>>>>>
>>>>>>>>> On 2019/10/9 9:19, Jackie Liu wrote:
>>>>>>>>>> __io_get_deferred_req is used to get all defer lists, including defer_list
>>>>>>>>>> and timeout_list, but io_sequence_defer should be only cares about the sequence.
>>>>>>>>>>
>>>>>>>>>> Signed-off-by: Jackie Liu <liuyun01@kylinos.cn>
>>>>>>>>>> ---
>>>>>>>>>>    fs/io_uring.c | 13 +++++--------
>>>>>>>>>>    1 file changed, 5 insertions(+), 8 deletions(-)
>>>>>>>>>>
>>>>>>>>>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>>>>>>>>>> index 8a0381f1a43b..8ec2443eb019 100644
>>>>>>>>>> --- a/fs/io_uring.c
>>>>>>>>>> +++ b/fs/io_uring.c
>>>>>>>>>> @@ -418,9 +418,7 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
>>>>>>>>>>    static inline bool io_sequence_defer(struct io_ring_ctx *ctx,
>>>>>>>>>>    				     struct io_kiocb *req)
>>>>>>>>>>    {
>>>>>>>>>> -	/* timeout requests always honor sequence */
>>>>>>>>>> -	if (!(req->flags & REQ_F_TIMEOUT) &&
>>>>>>>>>> -	    (req->flags & (REQ_F_IO_DRAIN|REQ_F_IO_DRAINED)) != REQ_F_IO_DRAIN)
>>>>>>>>>> +	if ((req->flags & (REQ_F_IO_DRAIN|REQ_F_IO_DRAINED)) != REQ_F_IO_DRAIN)
>>>>>>>>>>    		return false;
>>>>>>>>>>
>>>>>>>>>>    	return req->sequence != ctx->cached_cq_tail + ctx->rings->sq_dropped;
>>>>>>>>>> @@ -435,12 +433,11 @@ static struct io_kiocb *__io_get_deferred_req(struct io_ring_ctx *ctx,
>>>>>>>>>>    		return NULL;
>>>>>>>>>>
>>>>>>>>>>    	req = list_first_entry(list, struct io_kiocb, list);
>>>>>>>>>> -	if (!io_sequence_defer(ctx, req)) {
>>>>>>>>>> -		list_del_init(&req->list);
>>>>>>>>>> -		return req;
>>>>>>>>>> -	}
>>>>>>>>>> +	if (!(req->flags & REQ_F_TIMEOUT) && io_sequence_defer(ctx, req))
>>>>>>>>>> +		return NULL;
>>>>>>>>> Hi,
>>>>>>>>>
>>>>>>>>> For timeout req, we should also compare the sequence to determine to
>>>>>>>>> return NULL or the req. But now we will return req directly. Actually,
>>>>>>>>> no need to compare req->flags with REQ_F_TIMEOUT.
>>>>>>>>
>>>>>>>> Yes, not sure how I missed this, the patch is broken as-is. I will kill
>>>>>>>> it, cleanup can be done differently.
>>>>>>>
>>>>>>> Sorry for miss it, I don't wanna change the logic, it's not my
>>>>>>> original meaning.
>>>>>>
>>>>>> No worries, mistakes happen.
>>>>>>
>>>>>>> Personal opinion, timeout list should not be mixed with defer_list,
>>>>>>> which makes the code more complicated and difficult to understand.
>>>>>>
>>>>>> Not sure why you feel they are mixed? They are in separate lists, but
>>>>>> they share using the sequence logic. In that respet they are really not
>>>>>> that different, the sequence will trigger either one of them. Either as
>>>>>> a timeout, or as a "can now be issued". Hence the code handling them is
>>>>>> both shared and identical.
>>>>>
>>>>> I not sure, I think I need reread the code of timeout command.
>>>>>
>>>>>>
>>>>>> I do agree that the check could be cleaner, which is probably how the
>>>>>> mistake in this patch happened in the first place.
>>>>>>
>>>>>
>>>>> Yes, I agree with you. io_sequence_defer should be only cares about
>>>>> the sequence.  Thanks for point out this mistake.
>>>>
>>>> How about something like this? More cleanly separates them to avoid
>>>> mixing flags. The regular defer code will honor the flags, the timeout
>>>> code will just bypass those.
>>>>
>>>>
>>>> diff --git a/fs/io_uring.c b/fs/io_uring.c
>>>> index c92cb09cc262..4a2bb81cb1f1 100644
>>>> --- a/fs/io_uring.c
>>>> +++ b/fs/io_uring.c
>>>> @@ -416,26 +416,29 @@ static struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
>>>> 	return ctx;
>>>> }
>>>>
>>>> +static inline bool __io_sequence_defer(struct io_ring_ctx *ctx,
>>>> +				       struct io_kiocb *req)
>>>> +{
>>>> +	return req->sequence != ctx->cached_cq_tail + ctx->rings->sq_dropped;
>>>> +}
>>>> +
>>>> static inline bool io_sequence_defer(struct io_ring_ctx *ctx,
>>>> 				     struct io_kiocb *req)
>>>> {
>>>> -	/* timeout requests always honor sequence */
>>>> -	if (!(req->flags & REQ_F_TIMEOUT) &&
>>>> -	    (req->flags & (REQ_F_IO_DRAIN|REQ_F_IO_DRAINED)) != REQ_F_IO_DRAIN)
>>>> +	if ((req->flags & (REQ_F_IO_DRAIN|REQ_F_IO_DRAINED)) != REQ_F_IO_DRAIN)
>>>> 		return false;
>>>>
>>>> -	return req->sequence != ctx->cached_cq_tail + ctx->rings->sq_dropped;
>>>> +	return __io_sequence_defer(ctx, req);
>>>> }
>>>>
>>>> -static struct io_kiocb *__io_get_deferred_req(struct io_ring_ctx *ctx,
>>>> -					      struct list_head *list)
>>>> +static struct io_kiocb *io_get_deferred_req(struct io_ring_ctx *ctx)
>>>> {
>>>> 	struct io_kiocb *req;
>>>>
>>>> -	if (list_empty(list))
>>>> +	if (list_empty(&ctx->defer_list))
>>>> 		return NULL;
>>>>
>>>> -	req = list_first_entry(list, struct io_kiocb, list);
>>>> +	req = list_first_entry(&ctx->defer_list, struct io_kiocb, list);
>>>> 	if (!io_sequence_defer(ctx, req)) {
>>>> 		list_del_init(&req->list);
>>>> 		return req;
>>>> @@ -444,14 +447,20 @@ static struct io_kiocb *__io_get_deferred_req(struct io_ring_ctx *ctx,
>>>> 	return NULL;
>>>> }
>>>>
>>>> -static struct io_kiocb *io_get_deferred_req(struct io_ring_ctx *ctx)
>>>> -{
>>>> -	return __io_get_deferred_req(ctx, &ctx->defer_list);
>>>> -}
>>>> -
>>>> static struct io_kiocb *io_get_timeout_req(struct io_ring_ctx *ctx)
>>>> {
>>>> -	return __io_get_deferred_req(ctx, &ctx->timeout_list);
>>>> +	struct io_kiocb *req;
>>>> +
>>>> +	if (list_empty(&ctx->timeout_list))
>>>> +		return NULL;
>>>> +
>>>> +	req = list_first_entry(&ctx->timeout_list, struct io_kiocb, list);
>>>> +	if (!__io_sequence_defer(ctx, req)) {
>>>> +		list_del_init(&req->list);
>>>> +		return req;
>>>> +	}
>>>> +
>>>> +	return NULL;
>>>> }
>>>>
>>>> static void __io_commit_cqring(struct io_ring_ctx *ctx)
>>>>
>>>
>>> Much better, clearly and easy understand.
>>
>> Agree, this is easier to read as well, and harder to inadvertently
>> break. Can I add your reviewed-by to this one?
>>
>>
> 
> Yes, please, Reviewed-by: Jackie Liu <liuyun01@kylinos.cn>

Great thanks, now queued up.

-- 
Jens Axboe


      reply index

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-09  1:19 Jackie Liu
2019-10-09  1:19 ` [PATCH 2/2] io_uring: replace s->needs_lock with s->in_async Jackie Liu
2019-10-10 16:10   ` Jens Axboe
2019-10-10 16:10 ` [PATCH 1/2] io_uring: make the logic clearer for io_sequence_defer Jens Axboe
2019-10-11  2:24 ` yangerkun
2019-10-11  2:35   ` Jens Axboe
2019-10-11  3:06     ` Jackie Liu
2019-10-11  3:17       ` Jens Axboe
2019-10-11  3:26         ` Jens Axboe
2019-10-11  3:27         ` Jackie Liu
2019-10-11  3:34           ` Jens Axboe
2019-10-11  3:41             ` Jackie Liu
2019-10-11  3:42               ` Jens Axboe
2019-10-11  3:43                 ` Jackie Liu
2019-10-11  3:47                   ` Jens Axboe [this message]

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