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[80.11.63.14]) by smtp.gmail.com with ESMTPSA id r18sm1170198wme.48.2019.09.24.11.28.43 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 24 Sep 2019 11:28:45 -0700 (PDT) To: Jens Axboe , Peter Zijlstra Cc: Ingo Molnar , Ingo Molnar , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org References: <20190923083549.GA42487@gmail.com> <731b2087-7786-5374-68ff-8cba42f0cd68@kernel.dk> <759b9b48-1de3-1d43-3e39-9c530bfffaa0@kernel.dk> <43244626-9cfd-0c0b-e7a1-878363712ef3@gmail.com> <20190924094942.GN2349@hirez.programming.kicks-ass.net> <6f935fb9-6ebd-1df1-0cd0-69e34a16fa7e@kernel.dk> <29e6e06e-351f-c19d-ed7c-51f30c9ca887@kernel.dk> <08193e07-6f05-a496-492d-06ed8ce3aea1@gmail.com> <6228b13d-5ef6-e83e-b5dc-7a157013d43f@gmail.com> <79fa9cc2-e0cc-922f-89d3-9ace59abb2e8@gmail.com> <82f95b0f-8dd5-2fb5-7e17-b77072e86093@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 v2 0/2] Optimise io_uring completion waiting Message-ID: Date: Tue, 24 Sep 2019 21:28:37 +0300 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.1.0 MIME-Version: 1.0 In-Reply-To: <82f95b0f-8dd5-2fb5-7e17-b77072e86093@kernel.dk> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="MRerbCKMCgiDnv1pBgbZEOhd5eiJU1fgc" Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --MRerbCKMCgiDnv1pBgbZEOhd5eiJU1fgc Content-Type: multipart/mixed; boundary="1QZ07OeRFzsu9yWAYUl0GV7BUUUqSYMUc"; protected-headers="v1" From: Pavel Begunkov To: Jens Axboe , Peter Zijlstra Cc: Ingo Molnar , Ingo Molnar , linux-block@vger.kernel.org, linux-kernel@vger.kernel.org Message-ID: Subject: Re: [PATCH v2 0/2] Optimise io_uring completion waiting References: <20190923083549.GA42487@gmail.com> <731b2087-7786-5374-68ff-8cba42f0cd68@kernel.dk> <759b9b48-1de3-1d43-3e39-9c530bfffaa0@kernel.dk> <43244626-9cfd-0c0b-e7a1-878363712ef3@gmail.com> <20190924094942.GN2349@hirez.programming.kicks-ass.net> <6f935fb9-6ebd-1df1-0cd0-69e34a16fa7e@kernel.dk> <29e6e06e-351f-c19d-ed7c-51f30c9ca887@kernel.dk> <08193e07-6f05-a496-492d-06ed8ce3aea1@gmail.com> <6228b13d-5ef6-e83e-b5dc-7a157013d43f@gmail.com> <79fa9cc2-e0cc-922f-89d3-9ace59abb2e8@gmail.com> <82f95b0f-8dd5-2fb5-7e17-b77072e86093@kernel.dk> In-Reply-To: <82f95b0f-8dd5-2fb5-7e17-b77072e86093@kernel.dk> --1QZ07OeRFzsu9yWAYUl0GV7BUUUqSYMUc Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 24/09/2019 20:46, Jens Axboe wrote: > On 9/24/19 11:33 AM, Pavel Begunkov wrote: >> On 24/09/2019 16:13, Jens Axboe wrote: >>> On 9/24/19 5:23 AM, Pavel Begunkov wrote: >>>>> Yep that should do it, and saves 8 bytes of stack as well. >>>>> >>>>> BTW, did you test my patch, this one or the previous? Just curious = if it >>>>> worked for you. >>>>> >>>> Not yet, going to do that tonight >>> >>> Thanks! For reference, the final version is below. There was still a >>> signal mishap in there, now it should all be correct afaict. >>> >>> >>> diff --git a/fs/io_uring.c b/fs/io_uring.c >>> index 9b84232e5cc4..d2a86164d520 100644 >>> --- a/fs/io_uring.c >>> +++ b/fs/io_uring.c >>> @@ -2768,6 +2768,38 @@ static int io_ring_submit(struct io_ring_ctx *= ctx, unsigned int to_submit, >>> return submit; >>> } >>> =20 >>> +struct io_wait_queue { >>> + struct wait_queue_entry wq; >>> + struct io_ring_ctx *ctx; >>> + unsigned to_wait; >>> + unsigned nr_timeouts; >>> +}; >>> + >>> +static inline bool io_should_wake(struct io_wait_queue *iowq) >>> +{ >>> + struct io_ring_ctx *ctx =3D iowq->ctx; >>> + >>> + /* >>> + * Wake up if we have enough events, or if a timeout occured since = we >>> + * started waiting. For timeouts, we always want to return to users= pace, >>> + * regardless of event count. >>> + */ >>> + return io_cqring_events(ctx->rings) >=3D iowq->to_wait || >>> + atomic_read(&ctx->cq_timeouts) !=3D iowq->nr_timeouts; >>> +} >>> + >>> +static int io_wake_function(struct wait_queue_entry *curr, unsigned = int mode, >>> + int wake_flags, void *key) >>> +{ >>> + struct io_wait_queue *iowq =3D container_of(curr, struct io_wait_qu= eue, >>> + wq); >>> + >>> + if (!io_should_wake(iowq)) >>> + return -1; >> >> It would try to schedule only the first task in the wait list. Is that= the >> semantic you want? >> E.g. for waiters=3D[32,8] and nr_events =3D=3D 8, io_wake_function() r= eturns >> after @32, and won't wake up the second one. >=20 > Right, those are the semantics I want. We keep the list ordered by usin= g > the exclusive wait addition. Which means that for the case you list, > waiters=3D32 came first, and we should not wake others before that task= > gets the completions it wants. Otherwise we could potentially starve > higher count waiters, if we always keep going and new waiters come in. >=20 Yes. I think It would better to be documented in userspace API. I could imagine some crazy case deadlocking userspace. E.g.=20 thread 1: wait_events(8), reap_events thread 2: wait_events(32), wait(thread 1), reap_events works well Reviewed-by: Pavel Begunkov Tested-by: Pavel Begunkov BTW, I searched for wait_event*(), and it seems there are plenty of similar use cases. So, generic case would be useful, but this is for later. --=20 Yours sincerely, Pavel Begunkov --1QZ07OeRFzsu9yWAYUl0GV7BUUUqSYMUc-- --MRerbCKMCgiDnv1pBgbZEOhd5eiJU1fgc Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEE+6JuPTjTbx479o3OWt5b1Glr+6UFAl2KYFgACgkQWt5b1Glr +6WOVhAAoM1vm/5z41T0xHtzCKlfjOfoXADaUbIm74FJicLDi2PuwWgLvBnTApfO C0eONoA+Z4RmTU+Xw2Hkk9zU2MK79cdeDMPzNWr/oqHVac5gIn6xE2ykDjYppwGc 4O87BqVXz52AncaBoISCRNP7wYCOAW7KFicj+GUceCHsoDf4I/A45fWEXAPlgada Ouil+DKAtqK3KvwsVKtT3CBUSMuHSIRzKdiO6iC4AgEcf5haC+GEL0wZBzU8Y3h5 +xXsK8YMWYGTBPMR7TiDnXcW9WJf57xDqq5XoTlYVbG0vkRjrUVGhMJ+yAYtvy01 +I+IHQXk8Y/fnPC8IM75It7MJanNZ1vOKB6hy3XY40fKw7xWedEPIzyznmG70tou +klTXLNdA/DFQurOXtofvJhtzaRICMcyInT1pwPUG2+kNxxLKcBwBt3tDLQoAcQS aWkdPQBOJSQjThEi8REKK6UU2PdUSoF9/6lIGIbtgOrkxvnudS3QKGtYUUcrt82k rYakO+mqwJyrKh67B4Yj2GC/JSfVPVjd3ydrCGogxFokMX5iSwlYvf8MhAr92oh5 m76cOgr5QXJ94qu5KSEI4cXaHUdE+Vf/2wOXrsx0NeGZIf7foNbh/uvMwRVG5L1e 93acnuEGS4SGgQ4XPLe2MYEZ/ST6qtM9M5fVpQZiQj/UjRBiFCQ= =k2qf -----END PGP SIGNATURE----- --MRerbCKMCgiDnv1pBgbZEOhd5eiJU1fgc--