Re: [Qemu-devel] [PATCH v5 1/6] libnvdimm: nd_region flush callback support

[Christoph Hellwig]

On Thu, Apr 18, 2019 at 09:05:05AM -0700, Dan Williams wrote:
> > > I'd either add a comment about avoiding retpoline overhead here or just
> > > make ->flush == NULL mean generic_nvdimm_flush(). Just so that people 
> > > don't
> > > get confused by the code.
> >
> > Isn't this premature optimization?  I really don't like adding things
> > like this without some numbers to show it's worth it.
> 
> I don't think it's premature given this optimization technique is
> already being deployed elsewhere, see:
> 
> https://lwn.net/Articles/774347/

For one this one was backed by numbers, and second after feedback
from Linux we switched to the NULL pointer check instead.