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Wed, 12 Aug 2026 08:01:52 +0000 (GMT) Received: from [9.61.0.237] (unknown [9.61.0.237]) by smtpav04.dal12v.mail.ibm.com (Postfix) with ESMTP; Wed, 12 Aug 2026 08:01:52 +0000 (GMT) Message-ID: Date: Wed, 12 Aug 2026 13:31:51 +0530 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v7 4/9] nvme-multipath: add support for latency I/O policy To: John Garry , linux-nvme@lists.infradead.org Cc: hare@suse.de, kbusch@kernel.org, hch@lst.de, sagi@grimberg.me, dwagner@suse.de, kanie@linux.alibaba.com, jmeneghi@redhat.com, randyj@purestorage.com, martin.petersen@oracle.com, gjoyce@linux.ibm.com References: <20260809100825.2014133-1-nilay@linux.ibm.com> <20260809100825.2014133-5-nilay@linux.ibm.com> <2d0163f0-ecf3-4f59-9121-587f98eeb54c@oracle.com> <4e157ebe-7afd-45b9-9d35-f866b6f92097@linux.ibm.com> Content-Language: en-US From: Nilay Shroff In-Reply-To: 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-Spam-Details-Enc: AW1haW4tMjYwODEyMDA2MyBTYWx0ZWRfX2NLY8B0gHB+F 7HXR3iZPQfck/avRJvK91Z0J7kgj80UuY1dcXCa62RMC2f3ZtbYe7JBFWZeWioYGFSLI2ro+nzV nqkwTfhi0wPaJ6vNiKPHQeEaiOxSwX0MFvB709jwIQkkZTTT1ZcbEuHGD5j1TWNWFOJtBdb/Jd2 ykMYitfBFMEI4sBbx2dTzvoFvXYX0xyGm0dDEPDjA5U6jBas/fEjC4Dvfyan53jZ7rQOJ2BJgo6 bMmZgRHFC7LYtS3c+BsRLqNdXyqDL6+HbWaUgh/c0myga7ctRx5KYHCjKrjf/kmJFPO3Jt/uxac PhpRgt6ajEHyeKSMGbUQMsrJKc4MoDafKnwkeL9DHU024WniJ/hiTXK1rXMm7Gn+LHW/qSA04gs NDK97upSr57VUkbxYiorJeWzhik1pfKSRzNBrSiFr8+lcJUUoIlVEtP25MViFU3YF4JyInL3rhL y/V0dKIwxiSANqDIkmg== X-Proofpoint-Spam-Info: AW1haW4tMjYwODEyMDA2MyBTYWx0ZWRfX7MNZJklrFP8a 5KgxCUJn9RbHqTllo+iiVc8V+jzpbTCMw3FM4YaWrXMbbBTFrkML/E1eH48uOcGzssdIxfsLgTl BaD/P901o2YUyM0WcXJa7rwRJ1X4DFw= X-Authority-Analysis: v=2.4 cv=RqD16imK c=1 sm=1 tr=0 ts=6a7c2877 cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=IkcTkHD0fZMA:10 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=uAbxVGIbfxUO_5tXvNgY:22 a=wLyl8CQKQOLkDyj1Q1AA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: LQ__rjaPgoZVw0rKH7D__9aZGEUYAl-F X-Proofpoint-ORIG-GUID: Xn0IiFpd3P-pwgQX24MSEdLHvrpwnuZt X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.134,FMLib:17.12.100.49 definitions=2026-08-12_02,2026-08-10_03,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 phishscore=0 priorityscore=1501 suspectscore=0 lowpriorityscore=0 clxscore=1015 adultscore=0 bulkscore=0 malwarescore=0 impostorscore=0 spamscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608120063 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260812_010212_880323_7F03A965 X-CRM114-Status: GOOD ( 14.41 ) X-BeenThere: linux-nvme@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "Linux-nvme" Errors-To: linux-nvme-bounces+linux-nvme=archiver.kernel.org@lists.infradead.org On 8/11/26 3:56 PM, John Garry wrote: > On 10/08/2026 18:25, Nilay Shroff wrote: >>> >>> iops: (groupid=0, jobs=10): err= 0: pid=821: Mon Aug 10 08:08:28 2026 >>>     read: IOPS=9239, BW=36.1MiB/s (37.8MB/s)(1434MiB/39744msec) >>>       slat (usec): min=25, max=110836, avg=129.22, stdev=537.18 >>> >>> Note that I do have many heavy kernel debug options enabled, like kasan and kmemleak, which may influence this. >>> >> >> Thanks for testing. Given that you're running with KASAN, kmemleak, and other >> heavy debug options enabled, I think this is expected. Those configurations >> can significantly increase I/O completion latency, causing some samples to >> exceed the 1-second threshold. The warning is also rate-limited to avoid >> flooding the log. That said, still if it's causing a lot of noise in the logs >> then we could change it to dev_dbg_ratelimited() from dev_warn_ratelimited(). > > Note they these warnings go away when I turn off those debug options, as expected. > > The max latency I was seeing was ~1.2 seconds. Maybe you can just increase this limit for ignoring the sample. Or make it a dev_warn_once(). Or control the warn print rate with DEFINE_RATELIMIT_STATE. I think we could make it dev_warn_once() as we also increment the stat counter nr_ignored when we hit this case. So user could always interrogate the stat counter to find num of samples those were ignored. Thanks, --Nilay