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Thu, 14 Jan 2021 13:07:58 -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> <257c0977-2546-adeb-5e04-6b41ced792c7@gmail.com> <20210114004655.GA115522@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: <234af81b-2764-3e9e-6fb1-770877135ccc@gmail.com> Date: Thu, 14 Jan 2021 21:04:23 +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: <20210114004655.GA115522@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 14/01/2021 00:46, Marcelo Diop-Gonzalez wrote: > On Tue, Jan 12, 2021 at 08:47:11PM +0000, Pavel Begunkov wrote: >> 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(); > > Ah btw, so then we would have to add ->last_flush = seq in > io_timeout() too? I think that should be correct but just wanna make > sure that's what you meant. Because otherwise if list_empty() is true > for a while without updating ->last_flush then there could be > problems. Like for example if there are no timeouts for a while, and > seq == 2^32-2, then we add a timeout with off == 4. If last_flush is > still 0 then target-last_flush == 2, but seq - last_flush == 2^32-2 You've just answered your question :) You need to update it somehow, either unconditionally in commit, or in io_timeout(), or anyhow else. btw, I like your idea to do it in io_timeout(), because it adds a timeout anyway, so makes that list_empty() fails and kind of automatically pushes all that tracking. -- Pavel Begunkov