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=-5.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,UNPARSEABLE_RELAY, USER_AGENT_SANE_1 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 0B6FFC433DF for ; Wed, 8 Jul 2020 15:40:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id E67D0206DF for ; Wed, 8 Jul 2020 15:40:12 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730118AbgGHPkM (ORCPT ); Wed, 8 Jul 2020 11:40:12 -0400 Received: from out30-45.freemail.mail.aliyun.com ([115.124.30.45]:43727 "EHLO out30-45.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729022AbgGHPkM (ORCPT ); Wed, 8 Jul 2020 11:40:12 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R231e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e07425;MF=xiaoguang.wang@linux.alibaba.com;NM=1;PH=DS;RN=3;SR=0;TI=SMTPD_---0U27yzx8_1594222799; Received: from 192.168.124.22(mailfrom:xiaoguang.wang@linux.alibaba.com fp:SMTPD_---0U27yzx8_1594222799) by smtp.aliyun-inc.com(127.0.0.1); Wed, 08 Jul 2020 23:40:00 +0800 Subject: Re: [PATCH] io_uring: export cq overflow status to userspace To: Jens Axboe Cc: io-uring@vger.kernel.org, joseph.qi@linux.alibaba.com References: <83a3a0eb-8dea-20ad-ffc5-619226b47998@linux.alibaba.com> From: Xiaoguang Wang Message-ID: <54ce9903-4016-5b30-2fe9-397da9161bfe@linux.alibaba.com> Date: Wed, 8 Jul 2020 23:39:59 +0800 User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org hi, > On 7/7/20 11:29 PM, Xiaoguang Wang wrote: >> I modify above test program a bit: >> #include >> #include >> #include >> #include >> #include >> #include >> #include >> >> #include "liburing.h" >> >> static void test_cq_overflow(struct io_uring *ring) >> { >> struct io_uring_cqe *cqe; >> struct io_uring_sqe *sqe; >> int issued = 0; >> int ret = 0; >> int i; >> >> for (i = 0; i < 33; i++) { >> sqe = io_uring_get_sqe(ring); >> if (!sqe) { >> fprintf(stderr, "get sqe failed\n"); >> break;; >> } >> ret = io_uring_submit(ring); >> if (ret <= 0) { >> if (ret != -EBUSY) >> fprintf(stderr, "sqe submit failed: %d\n", ret); >> break; >> } >> issued++; >> } >> >> printf("issued requests: %d\n", issued); >> >> while (issued) { >> ret = io_uring_peek_cqe(ring, &cqe); >> if (ret) { >> if (ret != -EAGAIN) { >> fprintf(stderr, "peek completion failed: %s\n", >> strerror(ret)); >> break; >> } >> printf("left requets: %d %d\n", issued, IO_URING_READ_ONCE(*ring->sq.kflags)); >> continue; >> } >> io_uring_cqe_seen(ring, cqe); >> issued--; >> printf("left requets: %d\n", issued); >> } >> } >> >> int main(int argc, char *argv[]) >> { >> int ret; >> struct io_uring ring; >> >> ret = io_uring_queue_init(16, &ring, 0); >> if (ret) { >> fprintf(stderr, "ring setup failed: %d\n", ret); >> return 1; >> } >> >> test_cq_overflow(&ring); >> return 0; >> } >> >> Though with your patches applied, we still can not peek the last cqe. >> This test program will only issue 33 sqes, so it won't get EBUSY error. > > How about we make this even simpler, then - make the > IORING_SQ_CQ_OVERFLOW actually track the state, rather than when we fail > on submission. The liburing change would be the same, the kernel side > would then look like the below. > > > diff --git a/fs/io_uring.c b/fs/io_uring.c > index 4c9a494c9f9f..01981926cdf4 100644 > --- a/fs/io_uring.c > +++ b/fs/io_uring.c > @@ -1342,6 +1342,7 @@ static bool io_cqring_overflow_flush(struct io_ring_ctx *ctx, bool force) > if (cqe) { > clear_bit(0, &ctx->sq_check_overflow); > clear_bit(0, &ctx->cq_check_overflow); > + ctx->rings->sq_flags &= ~IORING_SQ_CQ_OVERFLOW; > } > spin_unlock_irqrestore(&ctx->completion_lock, flags); > io_cqring_ev_posted(ctx); > @@ -1379,6 +1380,7 @@ static void __io_cqring_fill_event(struct io_kiocb *req, long res, long cflags) > if (list_empty(&ctx->cq_overflow_list)) { > set_bit(0, &ctx->sq_check_overflow); > set_bit(0, &ctx->cq_check_overflow); > + ctx->rings->sq_flags |= IORING_SQ_CQ_OVERFLOW; > } > req->flags |= REQ_F_OVERFLOW; > refcount_inc(&req->refs); > @@ -6375,9 +6377,9 @@ static int io_sq_thread(void *data) > } > > /* Tell userspace we may need a wakeup call */ > + spin_lock_irq(&ctx->completion_lock); > ctx->rings->sq_flags |= IORING_SQ_NEED_WAKEUP; > - /* make sure to read SQ tail after writing flags */ > - smp_mb(); > + spin_unlock_irq(&ctx->completion_lock); > > to_submit = io_sqring_entries(ctx); > if (!to_submit || ret == -EBUSY) { > @@ -6400,7 +6402,9 @@ static int io_sq_thread(void *data) > } > finish_wait(&ctx->sqo_wait, &wait); > > + spin_lock_irq(&ctx->completion_lock); > ctx->rings->sq_flags &= ~IORING_SQ_NEED_WAKEUP; > + spin_unlock_irq(&ctx->completion_lock); > } > > mutex_lock(&ctx->uring_lock); > diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h > index 8d033961cb78..91953b543125 100644 > --- a/include/uapi/linux/io_uring.h > +++ b/include/uapi/linux/io_uring.h > @@ -198,6 +198,7 @@ struct io_sqring_offsets { > * sq_ring->flags > */ > #define IORING_SQ_NEED_WAKEUP (1U << 0) /* needs io_uring_enter wakeup */ > +#define IORING_SQ_CQ_OVERFLOW (1U << 1) /* app needs to enter kernel */ > > struct io_cqring_offsets { > __u32 head; > Looks good, I think it'll work now. I'll test and send patches soon, thanks. Regards, Xiaoguang Wang