Project "True 4x4"

[rcofell]

Hmmm, so you're certain it's due to the TLB bug and not how it's dealing with NUMA? Sort of curious how a software managed TLB would do, tho I don't know what the normal hit is for such... you could mess with Linux if you want to find out

An aside:
Chumbucket, a better comparison would be to the L1 Cache, if there's a miss then it'll be looking at a rather similar amount of cycles for either getting it from the L2 [, L3] or main memory. The reason for it being a better comparison is the page table is also a resident of memory*, it's just segregated to it's own spot and specialized (whereas L1 caches are for general program Instruction/Data bytewords which are used in a different context); so if the entry [from the page table] being requested not cached in the TLB then it'll have to take the slow route and go find it. Now the thing is just like the general caches, there should be a fairly low miss rate, so the delay shouldn't make too much of an impact in the grant scheme of things... unless there's a bug/workaround involved

*The reason I bring this up is because branch-prediction is just that, it predicts what's going to happen based on accumulated history, whereas a page table is just a bunch of entries saying each Effective[Virtual] address really points to this Real[Physical] address. The former deals with guessing where a computation(branch evaluation) will lead and pushes instructions into the pipeline ahead of time based on that, whereas E-A translation (page table lookup) is a strict correlation and must be looked up.

EDIT: hopefully this explanation reads through a little better...

Back to the issue:
I guess I never delved too deep into the Barcelona TLB bug, but I thought it was you either ran without the BIOS fix and it went pretty much full bore (for the architecture/implementation) with the risk of failure (freezing is what I remember hearing) under high load, or else you ran with the fix and encountered a 10-20% hit. I could be completely wrong on this, so if anyone knows please correct me.

I assume the BIOS feature you flipped puts you in the former situation (or latter, since you're disabling it??? confuses me now), hence I'm curious if it has to do with NUMA or some other part...