Re: [PATCH 4/6] nvme: zns: Add support for power_of_2 emulation to NVMe ZNS devices

Luis Chamberlain
2022-03-11T00:56:53Z

On Fri, Mar 11, 2022 at 08:50:47AM +0900, Damien Le Moal wrote:
> On 3/11/22 05:35, Luis Chamberlain wrote:
> > On Thu, Mar 10, 2022 at 06:43:47AM +0900, Damien Le Moal wrote:
> >> The indirect call using a function pointer makes the code obscure. And
> >> the cost of that call is far greater and always present compared to the
> >> CPU branch prediction which will luckily avoid most of the time taking
> >> the wrong branch of an if.
> >
> > The goal was to ensure no performance impact, and given a hot path
> > was involved and we simply cannot microbench append as there is no
> > way / API to do that, we can't be sure. But if you are certain that
> > there is no perf impact, it would be wonderful to live without it.
>
> Use zonefs. It uses zone append.

That'd be a microbench on zonefs append, not raw append, and so I
suspect a simple branch cannot make a difference and would get lost
as noise. So I don't think a perf test is required here. Please
let me know.

Luis