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Date:   Mon, 18 Mar 2019 16:21:34 -0600
From:   Keith Busch <kbusch@kernel.org>
To:     Nikhil Sambhus <nikhilsambhus@gmail.com>
Cc:     linux-block@vger.kernel.org
Subject: Re: Error while enabling io_poll for NVMe SSD
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On Mon, Mar 18, 2019 at 06:14:01PM -0400, Nikhil Sambhus wrote:
> Hi,
> 
> On a Linux Kernel 5.0.0+ machine (Ubuntu 16.04)  I am using the
> following command as a root user to enable polling for a NVMe SSD
> device.
> 
> # echo 1 > /sys/block/nvme2n1/queue/io_poll
> 
> I get the following error:
> 
> bash: echo: write error: Invalid argument
> 
> The current value of io_poll is 0.

Be sure to turn on the polling queues in the nvme driver. There are none
by default. The kernel parameter to that enable them is:

  nvme.poll_queues=X

Where 'X' is the number of polling queues. I'd recommend at least 1 per
CPU socket, but more is better.