Is my NVME too slow?

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Is my NVME too slow?

Helmut Jarausch-2
I have a very fast Samsung NVME drive hosting my root file system.
During backup 'atop' often shows 100% usage of my NVME drive while  
reading only a few MB/s and
several thousands 'Read' ops (during 10 seconds).

Is this normal or a measuring bug of 'atop'.

Stand alone timing tests have shown that this drive can read some GB  
per second.

What's happening?

Many thanks for a hint,
Helmut
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Re: Is my NVME too slow?

Alan Mackenzie
Hello, Helmut.

On Mon, Feb 04, 2019 at 12:01:33 +0100, Helmut Jarausch wrote:
> I have a very fast Samsung NVME drive hosting my root file system.
> During backup 'atop' often shows 100% usage of my NVME drive while  
> reading only a few MB/s and
> several thousands 'Read' ops (during 10 seconds).

> Is this normal or a measuring bug of 'atop'.

> Stand alone timing tests have shown that this drive can read some GB  
> per second.

> What's happening?

I don't understand this well myself, but please make sure you've got
CONFIG_PCI_MSI ("message signalled interrupts") enabled in your kernel.
This was a tip from Adam Carter to me in 2017-04, when my new Samsung
NVMe drive wasn't performing to expectations, and it helped greatly.

> Many thanks for a hint,
> Helmut

--
Alan Mackenzie (Nuremberg, Germany).