Optimization: keeping pointer all the time, or defining getter?

["Michael Büsch" <m@bues.ch>]

On Wed, 2011-05-11 at 18:34 +0200, Rafa? Mi?ecki wrote: 
> W dniu 11 maja 2011 18:27 u?ytkownik Michael B?sch <m@bues.ch> napisa?:
> > On Wed, 2011-05-11 at 18:22 +0200, Rafa? Mi?ecki wrote:
> >> I try to abstract bus in b43 driver. For frequently used fields
> >> solution is obvious:
> >> At init time I get info from bus-specific stuct and put it in generic field.
> >> Example: core revision. We often refer to it, I put it in abstraction struct.
> >>
> >> My question: what is the policy for cases with less frequently used fields?
> >> Example: I need to use "struct device" for registering some low lever stuff.
> >>
> >> I have two solutions:
> >>
> >> 1) Realtime:
> >> struct device *get_device(...)
> >> {
> >> if (dev->bus_type = B43_BUS_SSB)
> >> return dev->ssbdev->device;
> >> else if (dev->bus_type = B43_BUS_BCMA)
> >> return dev->bcmadev->device;
> >> }
> >>
> >> 2) Init time:
> >> void b43_ssb_init(struct ssb_device *ssbdev)
> >> {
> >> dev->struct = ssbdev->device;
> >> }
> >>
> >> The first one is slower but we don't keep "struct device" pointer in
> >> abstraction struct. Situation is opposite for the second one.
> >>
> >> Does anyone care? ;)
> >
> > Put a struct device pointer into b43_wldev.
> > The pointer is needed on every DMA transaction several times, so this
> > seems worth it.
> 
> Oops, OK, that was example. I thought DMA uses "dma_dev" frequently, not "dev".

Ah well. I don't know. Isn't dma_dev part of some SSB struct?

> But if we assume there is some not frequently used struct. What
> solution should be used then?

Apply common sense. ;)

-- 
Greetings Michael.