Messages in this thread | | | Date | Mon, 12 Jan 2009 23:50:41 +0100 | From | Ingo Molnar <> | Subject | Re: [patch] tlb flush_data: replace per_cpu with an array |
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* Andi Kleen <andi@firstfloor.org> wrote:
> > It is also slower (or so percpu.h says), and confusing I'd say. > > Well it's something like 3 instructions versus one. [...]
That's enough - micro-optimizations are done like that, instruction by instruction.
> [...] You would have a hard time benchmarking it unless you run it in a > very tight loop. It will be lost in the noise compared to all the other > costs of the IPI. > > Also why i don't like this patch is that on the typical small > single/dual core system running a 128 byte cache line distro kernel you > always pay the 1K cost now, while with per cpu it only needed one/two > entries.
4 or 8 cores is the norm these days - by the time this change hits real Linux computers en masse 8 cores will be quite common.
> Admittedly it could have been better commented. > > Not that it matters now unfortunately it's already applied. Sometimes > wonder why I still bother to do patch review...
Whether patches are already applied or not has no relevance - patches can still be undone or reverted of course, should your review feedback be correct.
Ingo
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