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Wed, 07 Apr 2021 04:45:53 -0700 (PDT) Subject: Re: [PATCH 2/3] io_uring: maintain drain logic for multishot requests To: Hao Xu , Jens Axboe Cc: io-uring@vger.kernel.org, Joseph Qi References: <1617794605-35748-1-git-send-email-haoxu@linux.alibaba.com> <1617794605-35748-3-git-send-email-haoxu@linux.alibaba.com> 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== Message-ID: <4d6f9688-4a8b-5fc6-f965-4903b5b82074@gmail.com> Date: Wed, 7 Apr 2021 12:41:46 +0100 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: <1617794605-35748-3-git-send-email-haoxu@linux.alibaba.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 07/04/2021 12:23, Hao Xu wrote: > Now that we have multishot poll requests, one sqe can emit multiple > cqes. given below example: > sqe0(multishot poll)-->sqe1-->sqe2(drain req) > sqe2 is designed to issue after sqe0 and sqe1 completed, but since sqe0 > is a multishot poll request, sqe2 may be issued after sqe0's event > triggered twice before sqe1 completed. This isn't what users leverage > drain requests for. > Here a simple solution is to ignore all multishot poll cqes, which means > drain requests won't wait those request to be done. > To achieve this, we should reconsider the req_need_defer equation, the > original one is: > > all_sqes(excluding dropped ones) == all_cqes(including dropped ones) > > this means we issue a drain request when all the previous submitted > sqes have generated their cqes. > Now we should ignore multishot requests, so: > all_sqes - multishot_sqes == all_cqes - multishot_cqes ==> > all_sqes + multishot_cqes - multishot_cqes == all_cqes > > Thus we have to track the submittion of a multishot request and the cqes > generation of it, including the ECANCELLED cqes. Here we introduce > cq_extra = multishot_cqes - multishot_cqes for it. > > There are other solutions like: > - just track multishot (non-ECNCELLED)cqes, don't track multishot sqes. > this way we include multishot sqes in the left end of the equation > this means we have to see multishot sqes as normal ones, then we > have to keep right one cqe for each multishot sqe. It's hard to do > this since there may be some multishot sqes which triggered > several events and then was cancelled, meanwhile other multishot > sqes just triggered events but wasn't cancelled. We still need to > track number of multishot sqes that haven't been cancelled, which > make things complicated > > For implementations, just do the submittion tracking in > io_submit_sqe() --> io_init_req() to make things simple. Otherwise if > we do it in per opcode issue place, then we need to carefully consider > each caller of io_req_complete_failed() because trick cases like cancel > multishot reqs in link. > > Signed-off-by: Hao Xu > --- > fs/io_uring.c | 16 +++++++++++++++- > 1 file changed, 15 insertions(+), 1 deletion(-) > > diff --git a/fs/io_uring.c b/fs/io_uring.c > index 192463bb977a..a7bd223ce2cc 100644 > --- a/fs/io_uring.c > +++ b/fs/io_uring.c > @@ -423,6 +423,7 @@ struct io_ring_ctx { > unsigned cq_mask; > atomic_t cq_timeouts; > unsigned cq_last_tm_flush; > + unsigned cq_extra; > unsigned long cq_check_overflow; > struct wait_queue_head cq_wait; > struct fasync_struct *cq_fasync; > @@ -879,6 +880,8 @@ struct io_op_def { > unsigned needs_async_setup : 1; > /* should block plug */ > unsigned plug : 1; > + /* set if opcode may generate multiple cqes */ > + unsigned multi_cqes : 1; > /* size of async data needed, if any */ > unsigned short async_size; > }; > @@ -924,6 +927,7 @@ struct io_op_def { > [IORING_OP_POLL_ADD] = { > .needs_file = 1, > .unbound_nonreg_file = 1, > + .multi_cqes = 1, > }, > [IORING_OP_POLL_REMOVE] = {}, > [IORING_OP_SYNC_FILE_RANGE] = { > @@ -1186,7 +1190,7 @@ static bool req_need_defer(struct io_kiocb *req, u32 seq) > if (unlikely(req->flags & REQ_F_IO_DRAIN)) { > struct io_ring_ctx *ctx = req->ctx; > > - return seq != ctx->cached_cq_tail > + return seq + ctx->cq_extra != ctx->cached_cq_tail > + READ_ONCE(ctx->cached_cq_overflow); > } > > @@ -1516,6 +1520,9 @@ static bool __io_cqring_fill_event(struct io_kiocb *req, long res, > > trace_io_uring_complete(ctx, req->user_data, res, cflags); > > + if (req->flags & REQ_F_MULTI_CQES) > + req->ctx->cq_extra++; > + Here we go, additional overhead burdening everyone but used for a little new feature. All that can be done in poll or in *_prep() on opcode by opcode basis. > /* > * If we can't get a cq entry, userspace overflowed the > * submission (by quite a lot). Increment the overflow count in > @@ -6504,6 +6511,13 @@ static int io_init_req(struct io_ring_ctx *ctx, struct io_kiocb *req, > req->result = 0; > req->work.creds = NULL; > > + if (sqe_flags & IOSQE_MULTI_CQES) { > + ctx->cq_extra--; > + if (!io_op_defs[req->opcode].multi_cqes) { > + return -EOPNOTSUPP; > + } > + } > + see above > /* enforce forwards compatibility on users */ > if (unlikely(sqe_flags & ~SQE_VALID_FLAGS)) { > req->flags = 0; > -- Pavel Begunkov