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    SubjectRe: [PATCH v5 1/6] libnvdimm: nd_region flush callback support
    On Fri, Apr 12, 2019 at 6:12 AM Jeff Moyer <jmoyer@redhat.com> wrote:
    >
    > Jan Kara <jack@suse.cz> writes:
    >
    > > 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.

    I don't think it's premature given this optimization technique is
    already being deployed elsewhere, see:

    https://lwn.net/Articles/774347/

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