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Tue, 25 Feb 2020 13:45:51 -0800 (PST) To: Jens Axboe , io-uring References: <1c5f074e-22dd-095a-6be7-730c81eeb1b1@kernel.dk> <82423419-1c14-418e-8085-2d8b902b0a2d@gmail.com> <71add82f-9d25-b879-5fe5-8e2a4eb26877@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: pick up link work on submit reference drop Message-ID: Date: Wed, 26 Feb 2020 00:45:02 +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: <71add82f-9d25-b879-5fe5-8e2a4eb26877@kernel.dk> Content-Type: multipart/signed; micalg=pgp-sha256; protocol="application/pgp-signature"; boundary="53pcYiuSQl4T7QRJYALhp9OlRJOKSSj4H" Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --53pcYiuSQl4T7QRJYALhp9OlRJOKSSj4H Content-Type: multipart/mixed; boundary="NyH80KWMHYOcHLy8BGQwKUtll30nANGV8"; protected-headers="v1" From: Pavel Begunkov To: Jens Axboe , io-uring Message-ID: Subject: Re: [PATCH] io_uring: pick up link work on submit reference drop References: <1c5f074e-22dd-095a-6be7-730c81eeb1b1@kernel.dk> <82423419-1c14-418e-8085-2d8b902b0a2d@gmail.com> <71add82f-9d25-b879-5fe5-8e2a4eb26877@kernel.dk> In-Reply-To: <71add82f-9d25-b879-5fe5-8e2a4eb26877@kernel.dk> --NyH80KWMHYOcHLy8BGQwKUtll30nANGV8 Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable On 26/02/2020 00:25, Jens Axboe wrote: > On 2/25/20 2:22 PM, Pavel Begunkov wrote: >> On 25/02/2020 23:27, Jens Axboe wrote: >>> If work completes inline, then we should pick up a dependent link ite= m >>> in __io_queue_sqe() as well. If we don't do so, we're forced to go as= ync >>> with that item, which is suboptimal. >>> >>> Signed-off-by: Jens Axboe >>> >>> --- >>> >>> diff --git a/fs/io_uring.c b/fs/io_uring.c >>> index ffd9bfa84d86..160cf1b0f478 100644 >>> --- a/fs/io_uring.c >>> +++ b/fs/io_uring.c >>> @@ -4531,8 +4531,15 @@ static void io_wq_submit_work(struct io_wq_wor= k **workptr) >>> } while (1); >>> } >>> =20 >>> - /* drop submission reference */ >>> - io_put_req(req); >>> + /* >>> + * Drop submission reference. In case the handler already dropped t= he >>> + * completion reference, then it didn't pick up any potential link >>> + * work. If 'nxt' isn't set, try and do that here. >>> + */ >>> + if (nxt) >> >> It can't even get here, because of the submission ref, isn't it? would= the >> following do? >> >> - io_put_req(req); >> + io_put_req_find_next(req, &nxt); >=20 > I don't think it can, let me make that change. And test. >=20 >> BTW, as I mentioned before, it appears to me, we don't even need compl= etion ref >> as it always pinned by the submission ref. I'll resurrect the patches = doing >> that, but after your poll work will land. >=20 > We absolutely do need two references, unfortunately. Otherwise we could= complete > the io_kiocb deep down the stack through the callback. And I need your knowledge here to not make mistakes :) I remember the conversation about the necessity of submission ref, that's= to make sure it won't be killed in the middle of block layer, etc. But what = about removing the completion ref then? E.g. io_read(), as I see all its work is bound by lifetime of io_read() c= all, so it's basically synchronous from the caller perspective. In other words= , it can't complete req after it returned from io_read(). And that would mean = it's save to have only submission ref after dealing with poll and other edge c= ases. Do I miss something? --=20 Pavel Begunkov --NyH80KWMHYOcHLy8BGQwKUtll30nANGV8-- --53pcYiuSQl4T7QRJYALhp9OlRJOKSSj4H Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIzBAEBCAAdFiEE+6JuPTjTbx479o3OWt5b1Glr+6UFAl5VlWIACgkQWt5b1Glr +6XmUQ//bMEv1GDaVkn759dZFFQNXq3oED4zStzb2b0ZCLr2TANdABI4PD/99T7I n4hiB7LaVKgK/rRVg7+L7byIgXQUmxTW6ifE2T0xhQ71G3tSTJsU/v9vlPtVqyhW kK7eSS91c0e8vfhs2xdLwT6N2HvPETQBCaoXcsh1IyRLWb9NmqOEhqA1ehHV/eE2 FCNf/3Cbpe0lwRCqynL1iiW7vVNf5Dl4KzQfaai7p/2eKpg9BW+0iWxkJoyvw1L4 Vr9x9FOGLnSmEgdFTH5ah+HKnr/qqU3x30oymfhGGKDRQRUClivyB0qB2R8NlAia 5uGamIUvJ3rPzwPTt1JW2Dzl7Z/WIKLA6Em5qVHnFOH5nm9MRMWtokDl7T49gW4Z FPO1FR9eDIy5d8ufXwX+96hGIa5oPPmdLAAI9jEPMnq0o35JD4u0bCCAjPSnOIx8 n15n5K+n+Mj3Rlys894hozp6enKxQrR7PZJEkDBr+D/47aXAL8D0jyR1vRGvXPYZ USdxHISoVIZN1AVGvg4NwaCTmS9uaqxeYwjXcT7JdMfIR2ovVKJ3rt24sZfvlQbk jn0VW5Kl5AWR/OkZt7A9e0EeuVX8EqhN1hRMsx2UmJC+4GD+sXBoUkgw0PhIjbZY BLTcMZiOEpSMOuxz5Vko4v114l1elfOqOb3JFNTeOOMWZKm8++I= =phwr -----END PGP SIGNATURE----- --53pcYiuSQl4T7QRJYALhp9OlRJOKSSj4H--