From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9EABCC47404 for ; Fri, 11 Oct 2019 03:43:50 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 736DC2089F for ; Fri, 11 Oct 2019 03:43:50 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726116AbfJKDnt convert rfc822-to-8bit (ORCPT ); Thu, 10 Oct 2019 23:43:49 -0400 Received: from smtpbguseast1.qq.com ([54.204.34.129]:37312 "EHLO smtpbguseast1.qq.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726108AbfJKDnt (ORCPT ); Thu, 10 Oct 2019 23:43:49 -0400 X-Greylist: delayed 2220 seconds by postgrey-1.27 at vger.kernel.org; Thu, 10 Oct 2019 23:43:48 EDT X-QQ-mid: bizesmtp17t1570765421t3fm104x Received: from [172.20.0.236] (unknown [218.76.23.26]) by esmtp6.qq.com (ESMTP) with id ; Fri, 11 Oct 2019 11:43:40 +0800 (CST) X-QQ-SSF: 00400000002000S0ZT90000A0000000 X-QQ-FEAT: 9nlJVcnIir7GemAxpdA4ETjjr2CqVF+pyTBhLkE43c3LMp93BhQmfByhHkf86 9MGD6I2cZLxyhKi6RfXF4Ti7cFmGMUbYCfLh3ew/EoE6IM0dTU0N7tmXWQzp1SO3mHY80Aj vc+ybjr6COzKO88i8gVj1Mji3UrZf/wOfWNZT3hbT1fwYiUviqFVCgugCIQ/vA5Z4DHmJG0 Gm/0TQgm/Lr6GENM0lWz2crq88vkPIDqVQQdA17+VBDOBie8bCO/D+Grv2jwgIcg/oNDymt hbVL8cdzLIV8pUDvd5kXb3UxGhhn4VUsq+27Dr2g5tBNBXj68KbG1FmcGKHecdxUIT+4ca+ ZtMZPFXkVH7hzP0ukEb3xR63AKfhL/5dI3bzH2Y X-QQ-GoodBg: 2 Content-Type: text/plain; charset=utf-8 Mime-Version: 1.0 (Mac OS X Mail 13.0 \(3594.4.19\)) Subject: Re: [PATCH 1/2] io_uring: make the logic clearer for io_sequence_defer From: Jackie Liu In-Reply-To: Date: Fri, 11 Oct 2019 11:43:40 +0800 Cc: yangerkun , linux-block@vger.kernel.org Content-Transfer-Encoding: 8BIT Message-Id: <71C4794E-2B1F-4A29-93E9-D578E71DECED@kylinos.cn> 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> To: Jens Axboe X-Mailer: Apple Mail (2.3594.4.19) X-QQ-SENDSIZE: 520 Feedback-ID: bizesmtp:kylinos.cn:qybgforeign:qybgforeign4 X-QQ-Bgrelay: 1 Sender: linux-block-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org > 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 -- BR, Jackie Liu