On Mon, Dec 22, 2008 at 12:49 PM, Rob OpenSuSE
The PAE works but starts to melt down at over 8GiB according to one LKML thread in which Linus called it a big mistake ever accepting it into the kernel. The SuSE pae kernel, appears to have similar config to the old SMP kernel "bigsmp". There's a lot of options chosen, which apply to medium-big server systems and not a typical dual core, or dual CPU box, with <= 4GiB RAM for unusual server (some very old) boxen.
Yeah, I remember using the SMP kernels back with 2.4.x IIRC. I have an old Dell Dual P3/Xeon machine that loaded it. Never needed the big kernel, so never played with it.
There's going to be overhead managing the larger memory addresses, and sometimes copying buffers into areas that 32bit PCI cards can read for DMA. The code complexity, must impact performance in the area of managing the VM page tables, it cannot be a 'Free Lunch' over simpler code.
That what I point out with 64bit systems. I remember back when some hand tuned 16bit code was faster than the new 32bit code.
Given all that, since the default kernel, gained the clever hack to patch in/out SMP or uniprocessor support, I've preferred to use that. I wonder what's compelling to make -pae the default, I suspect it's more that it'll work on more systemsm, rather than maximise performance for the majority of systems. Those NX capable CPUs have 64bit extentions, why not run them in that mode, and make use of extra registers and lose some of compatability cruft of i386?
Well, the Core Solo and Core Duos do support the NX bit and are 32bit. I probably need to do some benchmarks with both kernels on my P3 laptops to see what the difference is. -- To unsubscribe, e-mail: opensuse+unsubscribe@opensuse.org For additional commands, e-mail: opensuse+help@opensuse.org