linux-kernel - NVMe Poll CQ on timeout

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Message-ID: <MN2PR02MB633689DBBA6DE9DD7A34043FA5890@MN2PR02MB6336.namprd02.prod.outlook.com>
Date:   Thu, 19 Sep 2019 13:47:50 +0000
From:   Bharat Kumar Gogada <bharatku@...inx.com>
To:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>
CC:     Keith Busch <keith.busch@...ux.intel.com>,
        "keith.busch@...el.com" <keith.busch@...el.com>
Subject: NVMe Poll CQ on timeout

Hi All,

We are testing NVMe cards on ARM64 platform, the card uses MSI-X interrupts.
We are hitting following case in drivers/nvme/host/pci.c
/*
         * Did we miss an interrupt?
         */
        if (__nvme_poll(nvmeq, req->tag)) {
                dev_warn(dev->ctrl.device,
                         "I/O %d QID %d timeout, completion polled\n",
                         req->tag, nvmeq->qid);
                return BLK_EH_DONE;
        }

Can anyone tell when does nvme_timeout gets invoked ?
In what cases we see this interrupt miss ?

We are seeing this issue only for reads with following fio command 
fio --name=randwrite --ioengine=libaio --iodepth=1 --rw=randread --bs=128k --direct=0 \
--size=128M --numjobs=3 --group_reporting --filename=/dev/nvme0n1

We are not seeing issue with --rw=randwrite for same size.

Please let us know what can cause this issue. 

Regards,
Bharat