Messages in this thread | | | Date | Mon, 3 Jul 2006 09:56:21 -0700 (PDT) | From | Linus Torvalds <> | Subject | Re: [PATCH] genirq: ARM dyntick cleanup |
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On Mon, 3 Jul 2006, Andrew Morton wrote: > > void handle_dynamic_tick(struct irqaction *action) > { > } > > consumes one byte, doesn't it? That's not very far overboard ;)
Nope, it consumes - very fundamentally - about 64 bytes.
Even in the absense of alignment (which means that it generally takes up a minimum of 16 bytes of real memory), it takes up what would tend to be a much more critical resource: a cache line.
So an empty macro is a _lot_ more efficient than an empty function call.
For interrupt handlers, the L1 I$ miss rate is basically 100%. Even the L2 I$ miss rate is quite noticeable, _especially_ for things that are not easy to prefetch (ie stuff that is out-of-line). Which means that it also likely takes an inordinate amount of cycles, for doing zero work.
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