linux-kernel - Re: [GIT PULL 24/25] lightnvm: pblk: add iostat support

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Date:   Mon, 8 Jan 2018 03:54:57 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Matias Bjørling <m@...rling.me>
Cc:     Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Javier González <javier@...xlabs.com>
Subject: Re: [GIT PULL 24/25] lightnvm: pblk: add iostat support

On Fri, Jan 05, 2018 at 07:33:36PM +0100, Matias Bjørling wrote:
> On 01/05/2018 04:42 PM, Jens Axboe wrote:
> > On Fri, Jan 05 2018, Matias Bjørling wrote:
> > > From: Javier González <javier@...xlabs.com>
> > > 
> > > Since pblk registers its own block device, the iostat accounting is
> > > not automatically done for us. Therefore, add the necessary
> > > accounting logic to satisfy the iostat interface.
> > 
> > Ignorant question - why is it a raw block device, not using blk-mq?
> 
> The current flow is using the raw block device, together with the blk-mq
> nvme device driver. A bio is sent down to the nvme_nvm_submit_io() path in
> the /drivers/nvme/host/lightnvm.c file. From there it attaches the to NVMe
> blk-mq implementation.
> 
> Is there a better way to do it?

I suspect the right way to do things is to split NVMe for different
I/O command sets, and make this an I/O command set.

But before touching much of NVMe, I'd really, really like to see an
actual spec first.