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

Pankaj Gupta
2019-04-18T06:27:10Z

Hello,

Thank you for the suggestions on this.

>
> > On Thu 11-04-19 07:51:48, Dan Williams wrote:
> >> On Tue, Apr 9, 2019 at 9:09 PM Pankaj Gupta <pagupta@redhat.com> wrote:
> >> > + } else {
> >> > + if (nd_region->flush(nd_region))
> >> > + rc = -EIO;
> >>
> >> Given the common case wants to be fast and synchronous I think we
> >> should try to avoid retpoline overhead by default. So something like
> >> this:
> >>
> >> if (nd_region->flush == generic_nvdimm_flush)
> >> rc = generic_nvdimm_flush(...);
> >
> > 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.

Can we add the optimization after this version is merged.

Best regards,
Pankaj

>
> -Jeff
>
>