Re: Efficient IPC mechanism on Linux

[Arjan van de Ven <arjanv@redhat.com>]

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