AMD Bulldozer platform discussion

[DeadHead]

So basically there just trying to make OS think its a Intel with HT but that means the so called virtual cores will get used less .
kind of defeats getting 8 core processor . But I guess it does fix issues they had .

I both agree and disagree with this. Of course depending on usage, I do think that the way MS implemented this was in the best way possible - at this moment. When it comes to the applications that actually use several cores (quite a few comes to mind), this will allow full use of all eight cores. I can't see any better way for the scheduler to handle this new processor. Well, they could have (for that oh so important physcological effect!) skipped the idea to call it "4 cores: 8 logical" and instead just called them 8 physical cores, and just used core parking on every second core.

[bitsum.support]

If I were in Microsoft's shoes, I'd have likely done the same thing. This is indeed the best way to handle it without having to wait 6 months for a bunch of extensive new refactoring and regression testing of a critical part of the OS. Better to have done this than nothing, though some consumers are going to be a bit confused. Indeed, given the architecture of Bulldozer, I am starting to wonder if it isn't AMD's way of introducing HyperThreading without it being HyperThreading. Sure, they are full cores, but each pair share an L2 cache, share an FPU, and more .. making them 'Bulldozer modules', as AMD calls them.

When you read more about the Bulldozer architecture, e.g. here, it also describes the similarities (and differences) between a Bulldozer paired module of cores and an HT core: http://en.wikipedia.org/wiki/Bulldozer_(microarchitecture)

[bitsum.support]

Bulldozer Architecture from Wikipedia. Notice, in addition to benefiting from TurboCore by trying to keep things on every other CPU, the architecture of the Bulldozer platform is such that cores are paired together, with each pair sharing an L2, FPU, and other items. You definitely want to keep the load on every other module as long as possible. The below is an 8-way CPU, not 4 way. It is 4 pairs of cores.



UPDATE: Now, imagine arguing in court about whether this is HyperThreading or not? AMD seems in the clear, and now they can start sharing their computation resources, perhaps being the place they save money per-core - and the purpose for this change. To end users, the total core count is what is often seen, and AMD surely wants as many cores as they can get -- but can't step on the shoes of Intel's patented HyperThreading.

[DeadHead]

I'm a bit curious how this approach with this new scheduler compares the new Bulldozer to the older Phenom II X6 1090T in terms of performance.

[edkiefer]

I don't know about anyone else but what seems so odd to me is this new CPU architecture must of been in development for many yrs and it seems they waited for release to get the software end to work on OS's . Surely they could of worked with MS while it was in alpha, beta state just seems weird .

[bitsum.support]

I'm a bit curious how this approach with this new scheduler compares the new Bulldozer to the older Phenom II X6 1090T in terms of performance.

I didn't ever own the more expensive 1090T, but do have the cheaper little brother, the 1055T, and was going to run some tests. Sadly, the clock speed is a bit low for a comparison. I can tell you that after moving from a 1055T to a 8150, I sadly did not experience any perceived build speed improvements. There may have been a speed improvement, but not enough for me to notice. I still end up waiting forever for all of Process Lasso's editions to build, and for Process Lasso the CPU is the primary bottleneck. During about 85% of the build, all cores are maxed out. The remainder are single threaded operations.

The hotfix didn't apply to my 'highly threaded' scenario, but I suspect that *without* the hotfix, an average user would have been better off with the 1090T or 1055T. With the hotfix, the new processor should be a bit better, but it sure is no giant leap forward.

[edkiefer]

Some more info on this , Anandtech tests the hotfix run through some tests .

http://www.anandtech.com/show/5448/the-bulldozer-scheduling-patch-tested

[bitsum.support]

Thanks Ed, as always. I would like to quote their Final Words:

"AMD didn't overpromise as far as the benefits of these new scheduling/core parking hotfixes for Windows 7 are concerned. Single digit percentage gains can be expected in most mixed workloads, although there's a chance that you'd see low double digit gains if the conditions are right. It's important to note that the hotfixes for Windows 7 aren't ideal either. They simply force threads to be scheduled on empty modules first rather than idle cores on occupied modules. To properly utilize Bulldozer's architecture we'd need a scheduler that schedules both based on available cores/modules but biases its scheduling depending on data dependency between threads."

Source: http://www.anandtech.com/show/5448/the-bulldozer-scheduling-patch-tested/4

[edkiefer]

Yes, he goes into detail whats going on with the cores and set of cores . In end the beta Win8 also does better by few % too .

All that said if you compare dual, quad etc in Intels line up they seem to scale much better but that might just be the architect of the CPU itself and not so much a OS, schedule thing .

Edit: I hate to get to far off topic but I made a statement and wanted to check it .

found this site tested scaling of AMD and Intel chips in Linux , not in windows but still valid test, maybe better not being windows   

http://www.phoronix.com/scan.php?page=article&item=amd_bulldozer_scaling&num=1

[bitsum.support]

Thanks again, Ed. I figured someone would run some benchmarks in Linux, something I've advocated since this whole issue came up. The scheduler is so easily replaced, you can even run multiple tests with different schedulers to find out which is the most optimal. It is relevant because it shows the potential of the hardware, *if* the software is correct. In other words, it is relevant to give Microsoft a kick in the pants to make sure their scheduler is up to par. That said, they did issue these AMD Bulldozer hotfixes very quickly. Sure, they took a quick shortcut, but they made a big difference with it.

The one thing I wonder is if the updates have been pushed out yet via Windows Update, or if they will be. I would imagine they will.

[edkiefer]

I would assume once the hotfix is tested enough and brings no issues they will have it available under windows update .

[bitsum.support]

Yes, most likely, though we won't really know until it happens, if it has not already. Sometimes corporations don't follow the most intuitive of rational logic ;p.