








Both systems ran Windows 2003 R2, 64-bit.



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These chips could be in debug mode...
By extechman on 6/6/2007 5:27:09 PM , Rating: 2
I used to write system software for SGI, and when the new MIPS processors were coming out, we often had to run them in weird modes to work around a bug here or there. Some of them had some pretty substantial performance penalties, but the benefit of being able to find the next problem without respinning the chip made it worth it. At times, we had to turn off write buffers, shrink caches, put the chip in "in order" more, etc. AMD may be doing workarounds like those in this rev of silicon.

What I'm saying is that we still don't know anything about the performance of real Barcelona chips. Extrapolating the GHz won't give you the whole picture.

RE: These chips could be in debug mode...
By hstewarth on 6/7/2007 10:33:40 PM , Rating: 2
I think you might be confusing software with hardware. I don't believe that its same as software running in debug more than hardware. Most debugging on CPU's are done with ICE's which are done done with processor in realtime. I use such devices years ago debugging OS software.

Yes GHZ doesn't mean much.. it doesn't mean that Intel chip is 50% faster cpu than this chip. There is other factors like memory bus, cache and core instructionset.

Actuall with above in account and AMD Onboard memory controller and other things, I expect that this processor would do a lot better than it did.

By extechman on 6/14/2007 1:05:16 AM , Rating: 2
Hi, hstewarth

I was trying to be careful because I don't know exactly how this works on AMD CPUs, but what I meant was that in the CPUS I worked with (back in the day) there are a bunch of configuration bits that got clocked into the chip at startup to control its function. I believe that the same thing happens with modern x86 chips except that these bits come from the BIOS.

When we were debugging MIPS chips and new multiprocessor system architectures, we sometimes needed to change those configuration bits to tell the chip not to use certain performance features because they would cause the chip to produce incorrect results.

For example, if the chip was having trouble with cache coherent loads using an update protocol, we would switch the chip into invalidate mode - slower in some situations, but it worked. Or when the chips were new, we would have to make sure that the sysad bus (MIPS equivalent to FSB) ran at a particular fraction of the internal clock. Or we would have to disable out-of-order execution...

It's actually a lot like software debugging. It's all about testing as much logic as you can. You have to find as many bugs as you can before you spin the chip so sometimes you have to have to run at significantly lower performance just to get the OS to boot and run benchmarks properly. Then you fix a whole bunch of bugs and critical paths at the same time and respin the chip.

We don't know where AMD is in that process, but you'd have to hope that these chips are early silicon that was able to run correctly but had performance features turned off or not well tuned (what I soemwhat simplisticly referred to as "debug mode"). It's possible that the chips are being respun as we type.

If anyone would like to enlighten me on how AMD chips get configuration bits from the BIOS and what they control (do they still load microcode?), let me know!


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