On Fri, 2018-03-09 at 10:57 -0500, David Miller wrote: > From: David Woodhouse <dwmw2@xxxxxxxxxxxxx> > Date: Fri, 09 Mar 2018 15:31:15 +0000 > > > Eschewing a 15% speedup on the basis that "well, even though we've had > > three of these already for a decade, we're worried that adding a fourth > > might open the floodgates to further patches" does seem a little odd to > > me, FWIW. > > The cost we are dealing with is a fundamental one which is a result of > the hook design. > > Indirect calls are killer. > > Indirect calls are even more killer now in the age of Spectre and > retpolines. Imre's 15% measurement was, obviously, before that. We should redo it and confirm the numbers. > I definitely would rather see the fundamental issue addressed rather > than poking at it randomly with knobs for this case and that. Yeah. What do you think of the suggestion I made — that a given hook should automatically disable itself if it tautologically does nothing? Coupled with notifiers for when the rules change, to re-enable the hooks again? I confess I don't even know how realistic that is.
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