[RFC 1/3] nvme: skip block cgroups for passthrough commands

[Christoph Hellwig]

On Mon, May 01, 2023 at 08:33:04AM -0700, Keith Busch wrote:
> From: Keith Busch <kbusch at kernel.org>
> 
> Passthrough requests don't go through the submit_bio() path, so all the
> overhead of setting up the bio's cgroup is wasted cycles. Provide a path
> to skip this setup.

These days we should not need to set bi_bdev at all for passthrough,
so I think we can just drop the assingment.

But instead of just optimizing for passthrough we really need to optimize
this assignment and get rid of the cost entirely.  What is so expensive
about the cgroup lookup?  Is this even for a device that uses cgroups
at all, or could we come up with a flag to bypass all the lookup unless
cgroup are anbled?