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Fri, 26 Jun 2020 13:28:41 -0700 (PDT) To: Jens Axboe , io-uring References: <421c3b22-2619-a9a2-a76e-ed8251c7264c@kernel.dk> From: Pavel Begunkov Autocrypt: addr=asml.silence@gmail.com; prefer-encrypt=mutual; keydata= mQINBFmKBOQBEAC76ZFxLAKpDw0bKQ8CEiYJRGn8MHTUhURL02/7n1t0HkKQx2K1fCXClbps bdwSHrhOWdW61pmfMbDYbTj6ZvGRvhoLWfGkzujB2wjNcbNTXIoOzJEGISHaPf6E2IQx1ik9 6uqVkK1OMb7qRvKH0i7HYP4WJzYbEWVyLiAxUj611mC9tgd73oqZ2pLYzGTqF2j6a/obaqha +hXuWTvpDQXqcOZJXIW43atprH03G1tQs7VwR21Q1eq6Yvy2ESLdc38EqCszBfQRMmKy+cfp W3U9Mb1w0L680pXrONcnlDBCN7/sghGeMHjGKfNANjPc+0hzz3rApPxpoE7HC1uRiwC4et83 CKnncH1l7zgeBT9Oa3qEiBlaa1ZCBqrA4dY+z5fWJYjMpwI1SNp37RtF8fKXbKQg+JuUjAa9 Y6oXeyEvDHMyJYMcinl6xCqCBAXPHnHmawkMMgjr3BBRzODmMr+CPVvnYe7BFYfoajzqzq+h EyXSl3aBf0IDPTqSUrhbmjj5OEOYgRW5p+mdYtY1cXeK8copmd+fd/eTkghok5li58AojCba jRjp7zVOLOjDlpxxiKhuFmpV4yWNh5JJaTbwCRSd04sCcDNlJj+TehTr+o1QiORzc2t+N5iJ NbILft19Izdn8U39T5oWiynqa1qCLgbuFtnYx1HlUq/HvAm+kwARAQABtDFQYXZlbCBCZWd1 bmtvdiAoc2lsZW5jZSkgPGFzbWwuc2lsZW5jZUBnbWFpbC5jb20+iQJOBBMBCAA4FiEE+6Ju PTjTbx479o3OWt5b1Glr+6UFAlmKBOQCGwMFCwkIBwIGFQgJCgsCBBYCAwECHgECF4AACgkQ Wt5b1Glr+6WxZA//QueaKHzgdnOikJ7NA/Vq8FmhRlwgtP0+E+w93kL+ZGLzS/cUCIjn2f4Q Mcutj2Neg0CcYPX3b2nJiKr5Vn0rjJ/suiaOa1h1KzyNTOmxnsqE5fmxOf6C6x+NKE18I5Jy xzLQoktbdDVA7JfB1itt6iWSNoOTVcvFyvfe5ggy6FSCcP+m1RlR58XxVLH+qlAvxxOeEr/e aQfUzrs7gqdSd9zQGEZo0jtuBiB7k98t9y0oC9Jz0PJdvaj1NZUgtXG9pEtww3LdeXP/TkFl HBSxVflzeoFaj4UAuy8+uve7ya/ECNCc8kk0VYaEjoVrzJcYdKP583iRhOLlZA6HEmn/+Gh9 4orG67HNiJlbFiW3whxGizWsrtFNLsSP1YrEReYk9j1SoUHHzsu+ZtNfKuHIhK0sU07G1OPN 2rDLlzUWR9Jc22INAkhVHOogOcc5ajMGhgWcBJMLCoi219HlX69LIDu3Y34uIg9QPZIC2jwr 24W0kxmK6avJr7+n4o8m6sOJvhlumSp5TSNhRiKvAHB1I2JB8Q1yZCIPzx+w1ALxuoWiCdwV M/azguU42R17IuBzK0S3hPjXpEi2sK/k4pEPnHVUv9Cu09HCNnd6BRfFGjo8M9kZvw360gC1 reeMdqGjwQ68o9x0R7NBRrtUOh48TDLXCANAg97wjPoy37dQE7e5Ag0EWYoE5AEQAMWS+aBV IJtCjwtfCOV98NamFpDEjBMrCAfLm7wZlmXy5I6o7nzzCxEw06P2rhzp1hIqkaab1kHySU7g dkpjmQ7Jjlrf6KdMP87mC/Hx4+zgVCkTQCKkIxNE76Ff3O9uTvkWCspSh9J0qPYyCaVta2D1 Sq5HZ8WFcap71iVO1f2/FEHKJNz/YTSOS/W7dxJdXl2eoj3gYX2UZNfoaVv8OXKaWslZlgqN jSg9wsTv1K73AnQKt4fFhscN9YFxhtgD/SQuOldE5Ws4UlJoaFX/yCoJL3ky2kC0WFngzwRF Yo6u/KON/o28yyP+alYRMBrN0Dm60FuVSIFafSqXoJTIjSZ6olbEoT0u17Rag8BxnxryMrgR dkccq272MaSS0eOC9K2rtvxzddohRFPcy/8bkX+t2iukTDz75KSTKO+chce62Xxdg62dpkZX xK+HeDCZ7gRNZvAbDETr6XI63hPKi891GeZqvqQVYR8e+V2725w+H1iv3THiB1tx4L2bXZDI DtMKQ5D2RvCHNdPNcZeldEoJwKoA60yg6tuUquvsLvfCwtrmVI2rL2djYxRfGNmFMrUDN1Xq F3xozA91q3iZd9OYi9G+M/OA01husBdcIzj1hu0aL+MGg4Gqk6XwjoSxVd4YT41kTU7Kk+/I 5/Nf+i88ULt6HanBYcY/+Daeo/XFABEBAAGJAjYEGAEIACAWIQT7om49ONNvHjv2jc5a3lvU aWv7pQUCWYoE5AIbDAAKCRBa3lvUaWv7pfmcEACKTRQ28b1y5ztKuLdLr79+T+LwZKHjX++P 4wKjEOECCcB6KCv3hP+J2GCXDOPZvdg/ZYZafqP68Yy8AZqkfa4qPYHmIdpODtRzZSL48kM8 LRzV8Rl7J3ItvzdBRxf4T/Zseu5U6ELiQdCUkPGsJcPIJkgPjO2ROG/ZtYa9DvnShNWPlp+R uPwPccEQPWO/NP4fJl2zwC6byjljZhW5kxYswGMLBwb5cDUZAisIukyAa8Xshdan6C2RZcNs rB3L7vsg/R8UCehxOH0C+NypG2GqjVejNZsc7bgV49EOVltS+GmGyY+moIzxsuLmT93rqyII 5rSbbcTLe6KBYcs24XEoo49Zm9oDA3jYvNpeYD8rDcnNbuZh9kTgBwFN41JHOPv0W2FEEWqe JsCwQdcOQ56rtezdCJUYmRAt3BsfjN3Jn3N6rpodi4Dkdli8HylM5iq4ooeb5VkQ7UZxbCWt UVMKkOCdFhutRmYp0mbv2e87IK4erwNHQRkHUkzbsuym8RVpAZbLzLPIYK/J3RTErL6Z99N2 m3J6pjwSJY/zNwuFPs9zGEnRO4g0BUbwGdbuvDzaq6/3OJLKohr5eLXNU3JkT+3HezydWm3W OPhauth7W0db74Qd49HXK0xe/aPrK+Cp+kU1HRactyNtF8jZQbhMCC8vMGukZtWaAwpjWiiH bA== Subject: Re: [PATCH] io_uring: use task_work for links if possible Message-ID: Date: Fri, 26 Jun 2020 23:27:08 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.3.0 MIME-Version: 1.0 In-Reply-To: <421c3b22-2619-a9a2-a76e-ed8251c7264c@kernel.dk> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 25/06/2020 21:27, Jens Axboe wrote: > Currently links are always done in an async fashion, unless we > catch them inline after we successfully complete a request without > having to resort to blocking. This isn't necessarily the most efficient > approach, it'd be more ideal if we could just use the task_work handling > for this. > > Outside of saving an async jump, we can also do less prep work for > these kinds of requests. > > Running dependent links from the task_work handler yields some nice > performance benefits. As an example, examples/link-cp from the liburing > repository uses read+write links to implement a copy operation. Without > this patch, the a cache fold 4G file read from a VM runs in about > 3 seconds: A few comments below > > diff --git a/fs/io_uring.c b/fs/io_uring.c > index 0bba12e4e559..389274a078c8 100644 > --- a/fs/io_uring.c > +++ b/fs/io_uring.c > @@ -898,6 +898,7 @@ enum io_mem_account { ... > +static void __io_req_task_submit(struct io_kiocb *req) > +{ > + struct io_ring_ctx *ctx = req->ctx; > + > + __set_current_state(TASK_RUNNING); > + if (!io_sq_thread_acquire_mm(ctx, req)) { > + mutex_lock(&ctx->uring_lock); > + __io_queue_sqe(req, NULL, NULL); > + mutex_unlock(&ctx->uring_lock); > + } else { > + __io_req_task_cancel(req, -EFAULT); > + } > +} > + > +static void io_req_task_submit(struct callback_head *cb) > +{ > + struct io_kiocb *req = container_of(cb, struct io_kiocb, task_work); > + > + __io_req_task_submit(req); > +} > + > +static void io_req_task_queue(struct io_kiocb *req) > +{ > + struct task_struct *tsk = req->task; > + int ret; > + > + init_task_work(&req->task_work, io_req_task_submit); > + > + ret = task_work_add(tsk, &req->task_work, true); > + if (unlikely(ret)) { > + init_task_work(&req->task_work, io_req_task_cancel); Why not to kill it off here? It just was nxt, so shouldn't anything like NOCANCEL > + tsk = io_wq_get_task(req->ctx->io_wq); > + task_work_add(tsk, &req->task_work, true); > + } > + wake_up_process(tsk); > +} > + > static void io_free_req(struct io_kiocb *req) > { > struct io_kiocb *nxt = NULL; > @@ -1671,8 +1758,12 @@ static void io_free_req(struct io_kiocb *req) > io_req_find_next(req, &nxt); > __io_free_req(req); > > - if (nxt) > - io_queue_async_work(nxt); > + if (nxt) { > + if (nxt->flags & REQ_F_WORK_INITIALIZED) > + io_queue_async_work(nxt); Don't think it will work. E.g. io_close_prep() may have set REQ_F_WORK_INITIALIZED but without io_req_work_grab_env(). > + else > + io_req_task_queue(nxt); > + } > } > > static void io_wq_assign_next(struct io_wq_work **workptr, struct io_kiocb *nxt) > @@ -2013,12 +2104,6 @@ static void kiocb_end_write(struct io_kiocb *req) > file_end_write(req->file); > } > > -static inline void req_set_fail_links(struct io_kiocb *req) > -{ > - if ((req->flags & (REQ_F_LINK | REQ_F_HARDLINK)) == REQ_F_LINK) > - req->flags |= REQ_F_FAIL_LINK; > -} > - I think it'd be nicer in 2 patches, first moving io_sq_thread_drop_mm, etc. up. And the second one doing actual work. > static void io_complete_rw_common(struct kiocb *kiocb, long res, > struct io_comp_state *cs) > { > @@ -2035,35 +2120,6 @@ static void io_complete_rw_common(struct kiocb *kiocb, long res, > __io_req_complete(req, res, cflags, cs); > } > ... > switch (req->opcode) { > case IORING_OP_NOP: > @@ -5347,7 +5382,7 @@ static int io_req_defer(struct io_kiocb *req, const struct io_uring_sqe *sqe) > if (!req->io) { > if (io_alloc_async_ctx(req)) > return -EAGAIN; > - ret = io_req_defer_prep(req, sqe); > + ret = io_req_defer_prep(req, sqe, true); Why head of a link is for_async? > if (ret < 0) > return ret; > } > @@ -5966,7 +6001,7 @@ static void io_queue_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe, > ret = -EAGAIN; > if (io_alloc_async_ctx(req)) > goto fail_req; > - ret = io_req_defer_prep(req, sqe); > + ret = io_req_defer_prep(req, sqe, true); > if (unlikely(ret < 0)) > goto fail_req; > } > @@ -6022,13 +6057,14 @@ static int io_submit_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe, > if (io_alloc_async_ctx(req)) > return -EAGAIN; > > - ret = io_req_defer_prep(req, sqe); > + ret = io_req_defer_prep(req, sqe, false); > if (ret) { > /* fail even hard links since we don't submit */ > head->flags |= REQ_F_FAIL_LINK; > return ret; > } > trace_io_uring_link(ctx, req, head); > + io_get_req_task(req); > list_add_tail(&req->link_list, &head->link_list); > > /* last request of a link, enqueue the link */ > @@ -6048,7 +6084,7 @@ static int io_submit_sqe(struct io_kiocb *req, const struct io_uring_sqe *sqe, > if (io_alloc_async_ctx(req)) > return -EAGAIN; > > - ret = io_req_defer_prep(req, sqe); > + ret = io_req_defer_prep(req, sqe, true); > if (ret) > req->flags |= REQ_F_FAIL_LINK; > *link = req; > -- Pavel Begunkov