Re: [PATCH 00/27] Latest numa/core release, v16

[Linus Torvalds]

On Wed, Nov 21, 2012 at 7:10 AM, Ingo Molnar <mingo@xxxxxxxxxx> wrote:
>
> Because scalability slowdowns are often non-linear.

Only if you hold locks or have other non-cpu-private activity.

Which the vsyscall code really shouldn't have.

That said, it might be worth removing the "prefetchw(&mm->mmap_sem)"
from the VM fault path. Partly because software prefetches have never
ever worked on any reasonable hardware, and partly because it could
seriously screw up things like the vsyscall stuff.

I think we only turn prefetchw into an actual prefetch instruction on
3DNOW hardware. Which is the *old* AMD chips. I don't think even the
Athlon does that.

Anyway, it might be interesting to see a instruction-level annotated
profile of do_page_fault() or whatever

> So with CONFIG_NUMA_BALANCING=y we are taking a higher page
> fault rate, in exchange for a speedup.

The thing is, so is autonuma.

And autonuma doesn't show any of these problems. Autonuma didn't need
vsyscall hacks, autonuma didn't need TLB flushing optimizations,
autonuma just *worked*, and in fact got big speedups when Mel did the
exact same loads on that same machine, presumably with all the same
issues..

Why are you ignoring that fact?

                  Linus
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/