Messages in this thread |  | | From | David Howells <> | Subject | Re: [RFC] timers, pointers to functions and type safety | Date | Mon, 04 Dec 2006 12:22:44 +0000 |
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Ingo Molnar <mingo@elte.hu> wrote:
> the question is: which is more important, the type safety of a > container_of() [or type cast], which if we get it wrong produces a > /very/ trivial crash that is trivial to fix - or embedded timers data > structure size all around the kernel? I believe the latter is more > important.
Indeed yes.
Using container_of() and ditching the data value, you generally have to have one extra instruction per timer handler, if that, but you are able to discard one instruction or more from __run_timers() and struct timer_list discards a word.
You will almost certainly have far more timer_list structs in the kernel than timer handler functions, therefore it's a space win, and possibly also a time win (if the reduction of __run_timers() is greater than the increase in the timer handler).
And that extra instruction in the timer handler is usually going to be an addition or subtraction of a small immediate value - which may be zero (in which case the insn is dropped) or which may be folded directly into memory access instruction offsets.
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