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

Jeff Moyer
2019-04-12T13:12:44Z

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.

-Jeff