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Tue, 12 Jan 2021 12:50:45 -0800 (PST) To: Marcelo Diop-Gonzalez Cc: Jens Axboe , io-uring References: <20201219191521.82029-1-marcelo827@gmail.com> <20201219191521.82029-3-marcelo827@gmail.com> <20210108155726.GA8655@marcelo-debian.domain> 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 v2 2/2] io_uring: flush timeouts that should already have expired Message-ID: <257c0977-2546-adeb-5e04-6b41ced792c7@gmail.com> Date: Tue, 12 Jan 2021 20:47:11 +0000 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: <20210108155726.GA8655@marcelo-debian.domain> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 08/01/2021 15:57, Marcelo Diop-Gonzalez wrote: > On Sat, Jan 02, 2021 at 08:26:26PM +0000, Pavel Begunkov wrote: >> On 02/01/2021 19:54, Pavel Begunkov wrote: >>> On 19/12/2020 19:15, Marcelo Diop-Gonzalez wrote: >>>> Right now io_flush_timeouts() checks if the current number of events >>>> is equal to ->timeout.target_seq, but this will miss some timeouts if >>>> there have been more than 1 event added since the last time they were >>>> flushed (possible in io_submit_flush_completions(), for example). Fix >>>> it by recording the starting value of ->cached_cq_overflow - >>>> ->cq_timeouts instead of the target value, so that we can safely >>>> (without overflow problems) compare the number of events that have >>>> happened with the number of events needed to trigger the timeout. >> >> https://www.spinics.net/lists/kernel/msg3475160.html >> >> The idea was to replace u32 cached_cq_tail with u64 while keeping >> timeout offsets u32. Assuming that we won't ever hit ~2^62 inflight >> requests, complete all requests falling into some large enough window >> behind that u64 cached_cq_tail. >> >> simplifying: >> >> i64 d = target_off - ctx->u64_cq_tail >> if (d <= 0 && d > -2^32) >> complete_it() >> >> Not fond of it, but at least worked at that time. You can try out >> this approach if you want, but would be perfect if you would find >> something more elegant :) >> > > What do you think about something like this? I think it's not totally > correct because it relies on having ->completion_lock in io_timeout() so > that ->cq_last_tm_flushed is updated, but in case of IORING_SETUP_IOPOLL, > io_iopoll_complete() doesn't take that lock, and ->uring_lock will not > be held if io_timeout() is called from io_wq_submit_work(), but maybe > could still be worth it since that was already possibly a problem? > > diff --git a/fs/io_uring.c b/fs/io_uring.c > index cb57e0360fcb..50984709879c 100644 > --- a/fs/io_uring.c > +++ b/fs/io_uring.c > @@ -353,6 +353,7 @@ struct io_ring_ctx { > unsigned cq_entries; > unsigned cq_mask; > atomic_t cq_timeouts; > + unsigned cq_last_tm_flush; It looks like that "last flush" is a good direction. I think there can be problems at extremes like completing 2^32 requests at once, but should be ok in practice. Anyway better than it's now. What about the first patch about overflows and cq_timeouts? I assume that problem is still there, isn't it? See comments below, but if it passes liburing tests, please send a patch. > unsigned long cq_check_overflow; > struct wait_queue_head cq_wait; > struct fasync_struct *cq_fasync; > @@ -1633,19 +1634,26 @@ static void __io_queue_deferred(struct io_ring_ctx *ctx) > > static void io_flush_timeouts(struct io_ring_ctx *ctx) > { > + u32 seq = ctx->cached_cq_tail - atomic_read(&ctx->cq_timeouts); > + a nit, if (list_empty()) return; + do {} while(); timeouts can be rare enough > while (!list_empty(&ctx->timeout_list)) { > + u32 events_needed, events_got; > struct io_kiocb *req = list_first_entry(&ctx->timeout_list, > struct io_kiocb, timeout.list); > > if (io_is_timeout_noseq(req)) > break; > - if (req->timeout.target_seq != ctx->cached_cq_tail > - - atomic_read(&ctx->cq_timeouts)) > + extra new line > + events_needed = req->timeout.target_seq - ctx->cq_last_tm_flush; > + events_got = seq - ctx->cq_last_tm_flush; > + if (events_got < events_needed) probably <= > break; basically it checks that @target is in [last_flush, cur_seq], it can use such a comment + a note about underflows and using the modulus arithmetic, like with algebraic rings > > list_del_init(&req->timeout.list); > io_kill_timeout(req); > } > + > + ctx->cq_last_tm_flush = seq; > } > > static void io_commit_cqring(struct io_ring_ctx *ctx) > -- Pavel Begunkov