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

[Rafał Miłecki]

W dniu 11 maja 2011 18:27 użytkownik Michael Büsch <m at bues.ch> napisał:
> On Wed, 2011-05-11 at 18:22 +0200, Rafał Miłecki 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".

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

-- 
Rafał