Ingo Molnar <[email protected]> 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.
David
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