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Thu, 10 Oct 2019 20:47:06 -0700 (PDT) Subject: Re: [PATCH 1/2] io_uring: make the logic clearer for io_sequence_defer To: Jackie Liu Cc: yangerkun , linux-block@vger.kernel.org References: <20191009011959.2203-1-liuyun01@kylinos.cn> <7af32ce6-dc8f-6683-2b99-95eefb598bff@huawei.com> <597dc8a4-b9db-f0b7-21b5-12050f07e766@kernel.dk> <544E51DB-7774-4DDF-A897-7A957AE2CDEB@kylinos.cn> <6e1c1450-4317-7acf-dfa0-40977de4b8ea@kernel.dk> <543C3771-8956-40C4-B477-6B0F2FF477F5@kylinos.cn> <9C395F47-FE38-4E42-9DB0-3CCC427DE857@kylinos.cn> <71C4794E-2B1F-4A29-93E9-D578E71DECED@kylinos.cn> From: Jens Axboe Message-ID: <617f81c3-4633-e1b2-f51b-ae63fb071237@kernel.dk> Date: Thu, 10 Oct 2019 21:47:03 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <71C4794E-2B1F-4A29-93E9-D578E71DECED@kylinos.cn> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 10/10/19 9:43 PM, Jackie Liu wrote: > > >> 2019年10月11日 11:42，Jens Axboe 写道： >> >> On 10/10/19 9:41 PM, Jackie Liu wrote: >>> >>> >>>> 2019年10月11日 11:34，Jens Axboe 写道： >>>> >>>> On 10/10/19 9:27 PM, Jackie Liu wrote: >>>>> >>>>> >>>>>> 2019年10月11日 11:17，Jens Axboe 写道： >>>>>> >>>>>> On 10/10/19 9:06 PM, Jackie Liu wrote: >>>>>>> >>>>>>> >>>>>>>> 2019年10月11日 10:35，Jens Axboe 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 >>>>>>>>>> --- >>>>>>>>>> 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 Great thanks, now queued up. -- Jens Axboe