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[109.152.100.135]) by smtp.gmail.com with ESMTPSA id u5sm28753296wro.56.2020.11.18.06.20.19 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 18 Nov 2020 06:20:19 -0800 (PST) To: dongjoo seo Cc: Damien Le Moal , "hch@infradead.org" , "axboe@kernel.dk" , "ming.lei@redhat.com" , "linux-block@vger.kernel.org" , "sbates@raithlin.com" References: <20201118004746.GA29180@dongjoo-desktop> <20201118070714.GA3786@infradead.org> <310b9d38-1dde-b74e-f68f-32e8c7148336@gmail.com> <7F6FFFCB-3FD1-4A7B-8D30-FF4BBAD4AEA4@gmail.com> 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] blk-mq: modify hybrid sleep time to aggressive Message-ID: Date: Wed, 18 Nov 2020 14:17:13 +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: <7F6FFFCB-3FD1-4A7B-8D30-FF4BBAD4AEA4@gmail.com> Content-Type: text/plain; charset=windows-1252 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-block@vger.kernel.org On 18/11/2020 10:35, dongjoo seo wrote: > I agree with your opinion. And your patch is also good approach. > How about combine it? Adaptive solution with 3/4. I couldn't disclose numbers back then, but thanks to a steep skewed latency distribution of NAND/SSDs, it actually was automatically adjusting it to ~3/4 for QD1 and long enough requests (~75+ us). Also, if "max(sleep_ns, half_mean)" is removed, it was keeping the time below 1/2 for fast requests (less than ~30us), and that is a good thing because it was constantly oversleeping them. Though new ultra low-latency SSDs came since then. The real problem is to find anyone who actually uses it, otherwise it's just a chunk of dead code. Do you? Anyone? I remember once it was completely broken for months, but that was barely noticed. > Because, if we get the intensive workloads then we need to > decrease the whole cpu utilization even with [1]. > > [1] https://lkml.org/lkml/2019/4/30/117 > >> On Nov 18, 2020, at 6:26 PM, Pavel Begunkov wrote: >> >> On 18/11/2020 07:16, Damien Le Moal wrote: >>> On 2020/11/18 16:07, Christoph Hellwig wrote: >>>> Adding Damien who wrote this code. >>> >>> Nope. It wasn't me. I think it was Stephen Bates: >>> >>> commit 720b8ccc4500 ("blk-mq: Add a polling specific stats function") >>> >>> So +Stephen. >>>> >>>> On Wed, Nov 18, 2020 at 09:47:46AM +0900, Dongjoo Seo wrote: >>>>> Current sleep time for hybrid polling is half of mean time. >>>>> The 'half' sleep time is good for minimizing the cpu utilization. >>>>> But, the problem is that its cpu utilization is still high. >>>>> this patch can help to minimize the cpu utilization side. >> >> This won't work well. When I was experimenting I saw that half mean >> is actually is too much for fast enough requests, like <20us 4K writes, >> it's oversleeping them. Even more I'm afraid of getting in a vicious >> cycle, when oversleeping increases statistical mean, that increases >> sleep time, that again increases stat mean, and so on. That what >> happened for me when the scheme was too aggressive. >> >> I actually sent once patches [1] for automatic dynamic sleep time >> adjustment, but nobody cared. >> >> [1] https://lkml.org/lkml/2019/4/30/117 >> >>>>> >>>>> Below 1,2 is my test hardware sets. >>>>> >>>>> 1. Intel(R) Core(TM) i7-7700 CPU @ 3.60GHz + Samsung 970 pro 1Tb >>>>> 2. Intel(R) Core(TM) i7-5820K CPU @ 3.30GHz + INTEL SSDPED1D480GA 480G >>>>> >>>>> | Classic Polling | Hybrid Polling | this Patch >>>>> ----------------------------------------------------------------- >>>>> cpu util | IOPS(k) | cpu util | IOPS | cpu util | IOPS | >>>>> ----------------------------------------------------------------- >>>>> 1. 99.96 | 491 | 56.98 | 467 | 35.98 | 442 | >>>>> ----------------------------------------------------------------- >>>>> 2. 99.94 | 582 | 56.3 | 582 | 35.28 | 582 | >>>>> >>>>> cpu util means that sum of sys and user util. >>>>> >>>>> I used 4k rand read for this test. >>>>> because that case is worst case of I/O performance side. >>>>> below one is my fio setup. >>>>> >>>>> name=pollTest >>>>> ioengine=pvsync2 >>>>> hipri >>>>> direct=1 >>>>> size=100% >>>>> randrepeat=0 >>>>> time_based >>>>> ramp_time=0 >>>>> norandommap >>>>> refill_buffers >>>>> log_avg_msec=1000 >>>>> log_max_value=1 >>>>> group_reporting >>>>> filename=/dev/nvme0n1 >>>>> [rd_rnd_qd_1_4k_1w] >>>>> bs=4k >>>>> iodepth=32 >>>>> numjobs=[num of cpus] >>>>> rw=randread >>>>> runtime=60 >>>>> write_bw_log=bw_rd_rnd_qd_1_4k_1w >>>>> write_iops_log=iops_rd_rnd_qd_1_4k_1w >>>>> write_lat_log=lat_rd_rnd_qd_1_4k_1w >>>>> >>>>> Thanks >>>>> >>>>> Signed-off-by: Dongjoo Seo >>>>> --- >>>>> block/blk-mq.c | 3 +-- >>>>> 1 file changed, 1 insertion(+), 2 deletions(-) >>>>> >>>>> diff --git a/block/blk-mq.c b/block/blk-mq.c >>>>> index 1b25ec2fe9be..c3d578416899 100644 >>>>> --- a/block/blk-mq.c >>>>> +++ b/block/blk-mq.c >>>>> @@ -3749,8 +3749,7 @@ static unsigned long blk_mq_poll_nsecs(struct request_queue *q, >>>>> return ret; >>>>> >>>>> if (q->poll_stat[bucket].nr_samples) >>>>> - ret = (q->poll_stat[bucket].mean + 1) / 2; >>>>> - >>>>> + ret = (q->poll_stat[bucket].mean + 1) * 3 / 4; >>>>> return ret; >>>>> } >>>>> >>>>> -- >>>>> 2.17.1 >>>>> >>>> ---end quoted text--- >>>> >>> >>> >> >> -- >> Pavel Begunkov > > -- Pavel Begunkov