Re: Minutes from Feb 21 LSE Call

Martin J. Bligh
2003-02-22T23:00:46Z

>> OK, so now you've slid from talking about PCs to 2-way to 4-way ...
>> perhaps because your original arguement was fatally flawed.
>
> oh, come on. the issue is whether memory is fast and flat.
> most "scalability" efforts are mainly trying to code around the fact
> that any ccNUMA (and most 4-ways) is going to be slow/bumpy.

Scalability is not just NUMA machines by any stretch of the imagination.
It's 2x, 4x, 8x SMP as well.

> it is reasonable to worry that optimizations for imbalanced machines
> will hurt "normal" ones. is it worth hurting uni by 5% to give
> a 50% speedup to IBM's 32-way? I think not, simply because
> low-end machines are more important to Linux.

We would never try to propose such a change, and never have.
Name a scalability change that's hurt the performance of UP by 5%.
There isn't one.

> ccNUMA worst-case latencies are not much different from decent
> cluster (message-passing) latencies. getting an app to work on a cluster
> is a matter of programming will.

It's a matter of repeatedly reimplementing a bunch of stuff in userspace,
instead of doing things in kernel space once, properly, with all the
machine specific knowledge that's needed. It's *so* much easier to
program over a single OS image.

M.