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Tue, 26 May 2026 15:28:13 +0000 (GMT) Received: from ltc.linux.ibm.com (unknown [9.5.196.140]) by smtpav04.dal12v.mail.ibm.com (Postfix) with ESMTP; Tue, 26 May 2026 15:28:13 +0000 (GMT) Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Date: Tue, 26 May 2026 10:28:13 -0500 From: Wen Xiong To: yukuai@fygo.io Cc: Jens Axboe , linux-block@vger.kernel.org, tom.leiming@gmail.com, jmoyer@redhat.com, Gjoyce , wenxiong@us.ibm.com Subject: Re: Observing higher CPU utilization during random IO fio testing In-Reply-To: <043e357f-5b37-4e05-9433-271504fc1d30@fygo.io> References: <338169f719c77e4afe58f42e9760349e@linux.ibm.com> <1cb74987-34e2-422f-93cf-9174fe913538@kernel.dk> <043e357f-5b37-4e05-9433-271504fc1d30@fygo.io> Message-ID: <4ce7323fc4b02cdabc96c8443d373091@linux.ibm.com> X-Sender: wenxiong@linux.ibm.com Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-GUID: LVr-jCd-xKC084MO8zQ-KAT51Iz7y2WP X-Proofpoint-ORIG-GUID: Y1aoA-GO9ZffEfyUmOdrSuMlEbb6foBv X-Authority-Analysis: v=2.4 cv=QIJYgALL c=1 sm=1 tr=0 ts=6a15bc10 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=NGcC8JguVDcA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=lQJ2ouIgk1iEnd2pObUA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwNTI2MDEzMCBTYWx0ZWRfX3ZHrNUYSKLmc mB6xu5Go26AKWweXCMGADZp0ICvSDs4Xo34bZTZgQ2Xgqqz72+u32n4txGWM3kZYySHzY3LrsdI qkjNmsoSfLGRY7iyvpHu29n055R62jSgYZCUNtBbbYuRTlTFAAxG1bDyLRnCVmrDR0SSc4k+A57 2x37NEZU4oWIYwIWFb0pzrJAIzlaQXZIngY+JJHckA5Q2F51uGFcAZJBGYGYUqv8WIKPdawrOC0 opQgCz5KXGxHJGmRXbFl3jQNKhfxB08vz/cUpnfq9t54TGn3zwbHvv091ooFANQUj/ubwXM6UOx F4saz/uP986l3pQHl3Tk7VAfz1z2+5WfJp2PDLIAaXzVCNBOGZXvtZwc1OxFjC99ESOVOj7ZaFt b79WhH2My7Tu5TuAxPkvMqeXk3TIe04jyXYFkXmKJ4GMavcLflWnOQRYtL6g2uz1OeF6vdmQ7Sm jFlHsJ/JFCR8/riSLNA== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1143,Hydra:6.1.125,FMLib:17.12.100.49 definitions=2026-05-26_03,2026-05-26_03,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1011 priorityscore=1501 impostorscore=0 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 adultscore=0 spamscore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2605130000 definitions=main-2605260130 On 2026-05-25 00:28, Yu Kuai wrote: > Hi, > > 在 2026/5/22 5:52, Jens Axboe 写道: >>> - More IO scheduler interaction, forces requests through scheduler >>> instead of direct dispatch(direct dispatch to hardware queue) > I don't understand this point. Can you explain more? I think plug > should not matter if request go through scheduler or not. My understanding is: Random IO tests are more CPU intensive. Plug delays the dispatch IOs to hardware queue(quick way) directly. Plug submits multiple IO requests in a batch to defer submitting IO until calling blk_flush_plug(dispatch to hardware queue) or task gets scheduling. > > And I assume you're testing raw disk, because filesystems should > always enable plug. > Yes. FIO random IO tests over raw disks. > Yes, perf data will be helpful. And please show your test in details > and I'll > check if I can reproduce it. System config: 47 dedicate cores 120 GB memory PCIe4 2-Port 64Gb FC Adapter 64Gb FC switch FlashSystem: FS9500, 12 LUNs/FC port Below is fio config for rwmixread=100: [global] randrepeat=0 buffered=0 direct=1 norandommap=1 group_reporting=1 size=80g ioengine=libaio rw=randrw bs=4k iodepth=1 rwmixread=100 runtime=600 ramp_time=5 time_based=1 numjobs=20 [job1] filename=/dev/dm-2 [job2] filename=/dev/dm-3 ... 24 jobs in total. We collected some perf data. What kind of perf data you want? Let me know. Thanks, Wendy