Re: -mmX 4G patches feedback [numbers: how much performance impact]

[Andrea Arcangeli <andrea@suse.de>]

On Tue, Apr 06, 2004 at 07:24:31PM +0200, Ingo Molnar wrote:
> (anyway, feel free to reproduce and post contrary results here. The onus

I will run benchmarks as soon as I'm back from vacations. You didn't
post the modified benchmarks to produce any realistic load.

I will use the HINT to measure the slowdown on HZ=1000. It's an optimal
benchmark simulating userspace load at various cache sizes and it's
somewhat realistic.

Note also that the slowdown I expect wasn't of the order 10%, obviously,
I was expecting something between 1 and 2% which would be an *huge*
slowdown for any cpu bound app just for the timer irq, and I will try to
reproduce it on my 4-way xeon.

Regardless, even if HZ=1000 would run 1% faster (not 0.02% slower as you
measured) that changes nothing in terms of the 4:4 badness, the real
badness is for apps doing more than userspace pure calculations.

> is on you. And if you think i'm upset about your approach to this whole
> issue then you are damn right.)

the one upset should be the users running 30% slower with stuff like
mysql just because they own a 4/8G box. There's little interest from my
part to spend time on 4:4 stuff when things are so obvious (I want
however to try to benchmark the HZ=1000 with the hint).