Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
From:   Bharat Kumar Gogada <bharatku@xilinx.com>
To:     Keith Busch <keith.busch@linux.intel.com>
CC:     "linux-nvme@lists.infradead.org" <linux-nvme@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "keith.busch@intel.com" <keith.busch@intel.com>,
        "axboe@fb.com" <axboe@fb.com>, "hch@lst.de" <hch@lst.de>
Subject: RE: NVMe Poll CQ on timeout
Thread-Topic: NVMe Poll CQ on timeout
Thread-Index: AdPdbaKnll1ikIRyRXyNIhFzf8HT4wIYrQ9gABMa5QABjX+swA==
Date:   Tue, 15 May 2018 13:58:32 +0000
Message-ID: <BLUPR0201MB15052CE08EF4230487E8DEC8A5930@BLUPR0201MB1505.namprd02.prod.outlook.com>
References: <BLUPR0201MB1505A10C31E4E3A3BDF7BDBAA58E0@BLUPR0201MB1505.namprd02.prod.outlook.com>
 <BLUPR0201MB1505FC0425F87A1A8E6E50DAA59B0@BLUPR0201MB1505.namprd02.prod.outlook.com>
 <20180507160211.GE20686@localhost.localdomain>
In-Reply-To: <20180507160211.GE20686@localhost.localdomain>
Accept-Language: en-US
Content-Language: en-US
received-spf: None (protection.outlook.com: xilinx.com does not designate
 permitted sender hosts)
spamdiagnosticoutput: 1:99
spamdiagnosticmetadata: NSPM
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
X-MS-Exchange-CrossTenant-Network-Message-Id: 6c4d5024-6e45-471b-b13e-08d5ba6bf225
X-MS-Exchange-CrossTenant-originalarrivaltime: 15 May 2018 13:58:32.9216
 (UTC)
X-MS-Exchange-CrossTenant-fromentityheader: Hosted
X-MS-Exchange-CrossTenant-id: 657af505-d5df-48d0-8300-c31994686c5c
X-MS-Exchange-Transport-CrossTenantHeadersStamped: BLUPR0201MB1473
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org

> I recall we did observe issues like this when legacy interrupts were used=
, so
> the driver does try to use MSI/MSIx if possible.
>=20
> The nvme_timeout() is called from the block layer when the driver didn't
> provide a completion within the timeout (default is 30 seconds for IO,
> 60 seconds for admin).
>=20
> This message you're seeing means the device did indeed post a completion
> queue entry for the timed out command, but the driver believes it was nev=
er
> notified via interrupt to check the completion queue.
>=20
> This means either one of two things happened: the interrupt was raised pr=
ior
> to the completion queue entry being written, or the interrupt was never
> raised in the first place.
>=20
> It might be possible to determine which if you can read the values from
> /proc/irq/<irq#>/spurious and see if the "last_unhandled" aligns with the
> expected completion time.
>=20
Thanks keith. We are seeing the condition for transactions greater than 256=
 KB.
We did try increase IO timeout to 60sec but we still see issue.=20

We do see spurious interrupts as following:
count 53224
unhandled 15890
last_unhandled 4294917520 ms

If there are spurious interrupts, isn't the EP handler called more times=20
and this might help EP driver to process pending completions. (Because as p=
er the code in 4.14 EP
driver isn't checking any interrupt status register, it starts processing c=
ompletion queues immediately
in interrupt handler)

If we have spurious why do we still see completion polled ?

Regards,
Bharat


> > > Hi,
> > >
> > > We are testing NVMe cards on ARM64 platform, the card uses legacy
> > > interrupts.
> > > Intermittently 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_HANDLED;
> > >         }
> > >
> > > Can anyone tell when does nvme_timeout gets invoked ?
> > > What does "Did we miss an interrupt mean" ? Does it mean host
> > > missing to service a interrupt raised by EP card ?
> > >
> > > Regards,
> > > Bharat