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On Thu, 19 Dec 2002, Linus Torvalds wrote: > > So it's between 0-4 cycles on machines that take 200 - 1000 cycles for > just the system call overhead. Side note: I'd expect indirect calls - and especially the predictable ones, like this - to maintain competitive behaviour on CPU's. Even the P4, which usually has really bad worst-case behaviour for more complex instructions (just look at the 2000 cycles for a regular int80/iret and shudder) does a indirect call without huge problems. That's because indirect calls are actually very common, and to some degree getting _more_ so with the proliferation of OO languages (and I'm discounting the "indirect call" that is just a return statement - they've obviously always been common, but a return stack means that CPU optimizations for "ret" instructions are different from "real" indirect calls). So I don't worry about the indirection per se. I'd worry a lot more about some of the tricks people mentioned (ie the "pushl $0xfffff000 ; ret" approach probably sucks quite badly on some CPU's, simply because it does bad things to return stacks on modern CPU's - not necessarily visible in microbenchmarks, but..). Linus - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ | |||||||||
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