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Thu, 30 Jul 2020 09:28:07 -0700 (PDT) To: Jens Axboe , Kanchan Joshi Cc: Kanchan Joshi , viro@zeniv.linux.org.uk, bcrl@kvack.org, Matthew Wilcox , Christoph Hellwig , Damien Le Moal , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, linux-aio@kvack.org, io-uring@vger.kernel.org, linux-block@vger.kernel.org, linux-api@vger.kernel.org, SelvaKumar S , Nitesh Shetty , Javier Gonzalez References: <1595605762-17010-1-git-send-email-joshi.k@samsung.com> <1595605762-17010-7-git-send-email-joshi.k@samsung.com> <80d27717-080a-1ced-50d5-a3a06cf06cd3@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 v4 6/6] io_uring: add support for zone-append Message-ID: Date: Thu, 30 Jul 2020 19:26:10 +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: <80d27717-080a-1ced-50d5-a3a06cf06cd3@kernel.dk> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Sender: io-uring-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: io-uring@vger.kernel.org On 30/07/2020 19:13, Jens Axboe wrote: > On 7/30/20 10:08 AM, Pavel Begunkov wrote: >> On 27/07/2020 23:34, Jens Axboe wrote: >>> On 7/27/20 1:16 PM, Kanchan Joshi wrote: >>>> On Fri, Jul 24, 2020 at 10:00 PM Jens Axboe wrote: >>>>> >>>>> On 7/24/20 9:49 AM, Kanchan Joshi wrote: >>>>>> diff --git a/fs/io_uring.c b/fs/io_uring.c >>>>>> index 7809ab2..6510cf5 100644 >>>>>> --- a/fs/io_uring.c >>>>>> +++ b/fs/io_uring.c >>>>>> @@ -1284,8 +1301,15 @@ static void __io_cqring_fill_event(struct io_kiocb *req, long res, long cflags) >>>>>> cqe = io_get_cqring(ctx); >>>>>> if (likely(cqe)) { >>>>>> WRITE_ONCE(cqe->user_data, req->user_data); >>>>>> - WRITE_ONCE(cqe->res, res); >>>>>> - WRITE_ONCE(cqe->flags, cflags); >>>>>> + if (unlikely(req->flags & REQ_F_ZONE_APPEND)) { >>>>>> + if (likely(res > 0)) >>>>>> + WRITE_ONCE(cqe->res64, req->rw.append_offset); >>>>>> + else >>>>>> + WRITE_ONCE(cqe->res64, res); >>>>>> + } else { >>>>>> + WRITE_ONCE(cqe->res, res); >>>>>> + WRITE_ONCE(cqe->flags, cflags); >>>>>> + } >>>>> >>>>> This would be nice to keep out of the fast path, if possible. >>>> >>>> I was thinking of keeping a function-pointer (in io_kiocb) during >>>> submission. That would have avoided this check......but argument count >>>> differs, so it did not add up. >>> >>> But that'd grow the io_kiocb just for this use case, which is arguably >>> even worse. Unless you can keep it in the per-request private data, >>> but there's no more room there for the regular read/write side. >>> >>>>>> diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h >>>>>> index 92c2269..2580d93 100644 >>>>>> --- a/include/uapi/linux/io_uring.h >>>>>> +++ b/include/uapi/linux/io_uring.h >>>>>> @@ -156,8 +156,13 @@ enum { >>>>>> */ >>>>>> struct io_uring_cqe { >>>>>> __u64 user_data; /* sqe->data submission passed back */ >>>>>> - __s32 res; /* result code for this event */ >>>>>> - __u32 flags; >>>>>> + union { >>>>>> + struct { >>>>>> + __s32 res; /* result code for this event */ >>>>>> + __u32 flags; >>>>>> + }; >>>>>> + __s64 res64; /* appending offset for zone append */ >>>>>> + }; >>>>>> }; >>>>> >>>>> Is this a compatible change, both for now but also going forward? You >>>>> could randomly have IORING_CQE_F_BUFFER set, or any other future flags. >>>> >>>> Sorry, I didn't quite understand the concern. CQE_F_BUFFER is not >>>> used/set for write currently, so it looked compatible at this point. >>> >>> Not worried about that, since we won't ever use that for writes. But it >>> is a potential headache down the line for other flags, if they apply to >>> normal writes. >>> >>>> Yes, no room for future flags for this operation. >>>> Do you see any other way to enable this support in io-uring? >>> >>> Honestly I think the only viable option is as we discussed previously, >>> pass in a pointer to a 64-bit type where we can copy the additional >>> completion information to. >> >> TBH, I hate the idea of such overhead/latency at times when SSDs can >> serve writes in less than 10ms. Any chance you measured how long does it > > 10us? :-) Hah, 10us indeed :) > >> take to drag through task_work? > > A 64-bit value copy is really not a lot of overhead... But yes, we'd > need to push the completion through task_work at that point, as we can't > do it from the completion side. That's not a lot of overhead, and most > notably, it's overhead that only affects this particular type. > > That's not a bad starting point, and something that can always be > optimized later if need be. But I seriously doubt it'd be anything to > worry about. I probably need to look myself how it's really scheduled, but if you don't mind, here is a quick question: if we do work_add(task) when the task is running in the userspace, wouldn't the work execution wait until the next syscall/allotted time ends up? -- Pavel Begunkov