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Mon, 10 Aug 2026 17:25:23 +0000 (GMT) Received: from [9.43.109.88] (unknown [9.43.109.88]) by smtpav02.wdc07v.mail.ibm.com (Postfix) with ESMTP; Mon, 10 Aug 2026 17:25:23 +0000 (GMT) Message-ID: <4e157ebe-7afd-45b9-9d35-f866b6f92097@linux.ibm.com> Date: Mon, 10 Aug 2026 22:55:21 +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> Content-Language: en-US From: Nilay Shroff In-Reply-To: <2d0163f0-ecf3-4f59-9121-587f98eeb54c@oracle.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-Authority-Analysis: v=2.4 cv=AMtp2X5w c=1 sm=1 tr=0 ts=6a7a098a cx=c_pps a=GFwsV6G8L6GxiO2Y/PsHdQ==:117 a=GFwsV6G8L6GxiO2Y/PsHdQ==:17 a=IkcTkHD0fZMA:10 a=Sv0fKeRqtYgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=Y2IxJ9c9Rs8Kov3niI8_:22 a=1xIkWWgTLhsQZ9xoJ6sA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: tqzgtmz8KwAJ1UEBDtN0xd_m0K68twnE X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwODEwMDE0NiBTYWx0ZWRfX03YP1i+xW9Lk eQyxSAcpoBBx+lLo6l8iRPS3+kgLx9XsuyPIiNQK3/hMXEEf1e1WjF5eFDmdOOlxsDf+CA5vdSy PQdJhG5QJwevITKRlZgDxDgfwXjDPWNOcOzjQEJ20cvU138vuN04PSm5HCIJ9njnXOkd2JIL8+a cBwhdKxdrBoDL4836qsnWnDrufwXThIffEZ0URcLiXBvUFzugk/V4xW4RPh89oyVe310M0My4bp np7QNe7DtJZgyvLfkSKdFOAFiGEpdHOGtv/sPSzFZBbWWmb8Bb0icPXWLKRrGPPd1kX1ZSPx12A Fti83Lwnf1hd0pTxaIWIjXaQdEQ1o0cvC1XlLorKZw51ws2CaaP02Vu1C2zcFwmefNAhBLV9aGc G5efs5g2GTp39hni2cgUMS3OBn4Xn4G2BpSo5FQh3WwyfWJYz+JWMsUEyKdeAtQjvvo8ow+FI1Y db9f8GSJuC+Dc76DqrA== X-Proofpoint-ORIG-GUID: y48Uf9HcHvCw3PnJO54kiluBfRtxLjgS X-Proofpoint-Spam-Info: AW1haW4tMjYwODEwMDE0NiBTYWx0ZWRfXzcE4AanL0ySe grOy0caP+JEHqg8ajApnCFWP0zd+/6D75iTaVqEOCBAVrCYXhqV6dZzLmBN81ziAn97lQ3OQRMk ZFx7lMuVGgU3e0JrG4pOWPUqf7Cb8TE= 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=2026-08-10_04,2026-08-10_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 adultscore=0 lowpriorityscore=0 clxscore=1015 priorityscore=1501 impostorscore=0 phishscore=0 spamscore=0 bulkscore=0 malwarescore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2606150000 definitions=main-2608100146 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.9.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20260810_102544_563554_FC945AE5 X-CRM114-Status: GOOD ( 18.88 ) 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 8/10/26 1:42 PM, John Garry wrote: > On 09/08/2026 11:07, Nilay Shroff wrote: >> +    /* >> +     * If latency > ~1s then ignore this sample to prevent EWMA from being >> +     * skewed by pathological outliers (multi-second waits, controller >> +     * timeouts etc.). This keeps path scores representative of normal >> +     * performance and avoids instability from rare spikes. If such high >> +     * latency is real, ANA state reporting or keep-alive error counters >> +     * will mark the path unhealthy and remove it from the head node list, >> +     * so we safely skip such sample here. >> +     */ >> +    if (unlikely(latency > NSEC_PER_SEC)) { >> +        stat->nr_ignored++; >> +        dev_warn_ratelimited(ns->ctrl->device, >> +            "ignoring sample with >1s latency (possible controller stall or timeout)\n"); >> +        return; >> +    } > > JFYI, I gave this series a spin and I see this warn a lot: > > # ./fio_read.sh nvme1n1 > iops: (g=0): rw=read, bs=(R) 4096B-4096B, (W) 4096B-4096B, (T) > 4096B-4096B, ioengine=libaio, iodepth=100 > ... > fio-3.38 > Starting 10 processes > [  130.005374] nvme_mpath_add_sample: 29 callbacks suppressed03h:08m:36s] > [  130.005387] nvme nvme2: ignoring sample with >1s latency (possible > controller stall or timeout) > [  130.009968] nvme nvme2: ignoring sample with >1s latency (possible > controller stall or timeout) > [  130.013176] nvme nvme2: ignoring sample with >1s latency (possible > controller stall or timeout) > [  130.019576] nvme nvme2: ignoring sample with >1s latency (possible > controller stall or timeout) > [  130.022275] nvme nvme2: ignoring sample with >1s latency (possible > controller stall or timeout) > [  130.024762] nvme nvme2: ignoring sample with >1s latency (possible > controller stall or timeout) > [  130.027268] nvme nvme2: ignoring sample with >1s latency (possible > controller stall or timeout) > [  130.130140] nvme nvme2: ignoring sample with >1s latency (possible > controller stall or timeout) > [  130.132316] nvme nvme2: ignoring sample with >1s latency (possible > controller stall or timeout) > [  130.139279] nvme nvme2: ignoring sample with >1s latency (possible > controller stall or timeout) > ^Cbs: 10 (f=10): [R(10)][0.4%][r=35.8MiB/s][r=9171 IOPS][eta 03h:07m:44s] > fio: terminating on signal 2 > > 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(). Thanks, --Nilay