Messages in this thread | | | Date | Wed, 10 Sep 2003 12:07:29 +0200 | From | Arjan van de Ven <> | Subject | Re: Efficient IPC mechanism on Linux |
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On Wed, Sep 10, 2003 at 10:52:55AM +0100, Jamie Lokier wrote: > Arjan van de Ven wrote: > > > The overhead implied by a memcpy() is the same, in the oder of magnitude, > > > ***whatever*** kernel version you can develop. > > > > yes a copy of a page is about 3000 to 4000 cycles on an x86 box in the > > uncached case. A pagetable operation (like the cpu setting the accessed > > or dirty bit) is in that same order I suspect (maybe half this, but not > > a lot less). Changing pagetable content is even more because all the > > tlb's and internal cpu state will need to be flushed... which is also a > > microcode operation for the cpu. And it's deadly in an SMP environment. > > I have just done a measurement on a 366MHz PII Celeron
This test is sort of the worst case against my argument: 1) It's a cpu with low memory bandwidth 2) It's a 1 CPU system 3) It's a pII not pIV; the pII is way more efficient cycle wise for pagetable operations
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