> > Dan Williams <dan.j.williams@xxxxxxxxx> writes: > > > On Mon, Apr 22, 2019 at 8:59 AM Jeff Moyer <jmoyer@xxxxxxxxxx> wrote: > >> > >> Dan Williams <dan.j.williams@xxxxxxxxx> writes: > >> > >> > On Thu, Apr 18, 2019 at 9:18 AM Christoph Hellwig <hch@xxxxxxxxxxxxx> > >> > wrote: > >> >> > >> >> 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. > >> > > >> > Ok I should have noticed the switch to NULL pointer check. However, > >> > the question still stands do we want everyone to run numbers to > >> > justify this optimization, or make it a new common kernel coding > >> > practice to do: > >> > > >> > if (!object->op) > >> > generic_op(object); > >> > else > >> > object->op(object); > >> > > >> > ...in hot paths? > >> > >> I don't think nvdimm_flush is a hot path. Numbers of some > >> representative workload would prove one of us right. > > > > I'd rather say that the if "if (!op) do_generic()" pattern is more > > readable in the general case, saves grepping for who set the op in the > > common case. The fact that it has the potential to be faster is gravy > > at that point. > > If the primary motivation is performance, then I'd expect performance > numbers to back it up. If that isn't the primary motivation, then > choose whichever way you feel is appropriate. Agree. This change enhances the code readability. Will add this change in v6 with other changes. Thank you! Pankaj > > Cheers, > Jeff >
