Re: 2.2.18Pre Lan Performance Rocks!

Ingo Molnar
2000-10-30T07:17:32Z

On Mon, 30 Oct 2000, Andi Kleen wrote:

> One problem in Linux 2.2 is that kernel threads reload their VM on
> context switch (that would include the nfsd thread), this should be
> fixed in 2.4 with lazy mm. Hmm actually it should be only fixed for
> true kernel threads that have been started with kernel_thread(), the
> "pseudo kernel threads" like nfsd uses probably do not get that
> optimization because they don't set their MM to init_mm.

yes, but for this there is an explicit mechanizm to lazy-MM during lengthy
system calls, an example is in buffer.c:

user_mm = start_lazy_tlb();
error = sync_old_buffers();
end_lazy_tlb(user_mm);

> > to get disproportiantely higher in Linux than NetWare 5.x and when it hits
> > 60% of total clock cycles, Linux starts dropping off. NetWare 5.x is 1/8
>
> I think that can be explained by the copying.

yes. Constant copying contaminates the L1/L2 caches and creates dirty
cachelines all around the place. Fixed in 2.4 + TUX ;-)

Ingo