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If you look at SPEC CPU benchmark, Itanium was not bad at all in terms of instructions-per-cycle. IIRC in fp performance it could beat Netburst Pentium4 running

If you look at SPEC CPU benchmark, Itanium was not bad at all in terms of instructions-per-cycle. IIRC in fp performance it could beat Netburst Pentium4 running twice its clock speed, and even compared favorably to Core. I.e. if Intel produced Itaniums which ran at the same clock speed as Core CPUs, it would be world's fastest single-threaded number cruncher. So I don't really buy the "Itanium is bad architecture" story. It's fate was probably decided around 1999-2000. At that point Itanium was still pretty good against Pentium 3 and Pentium 4. And name "IA-64" indicates Intel didn't plan to make 64-bit Pentiums. So eventually Pentiums would fill low-end segment while the rest would be occupied by 64-bit Itaniums. AMD killed that plan by releasing AMD64 architecture. It was an obvious upgrade to x86, so it would clearly do better in the market than IA-64. So Intel decided to go for x86-64 too, and Itanium was doomed at that point. They didn't even bother making Itaniums with same clock speed as Xeons. So it's definitely possible that if AMD decided to stick to 32 bits at that time, Intel would have pushed optimized IA-64. Also AMD64 could be worse than it is. E.g. if they decided to increase only register size but keep the number of registers the same, IA-64 could still come on top.

giantrobot 4y ago
> AMD killed that plan by releasing AMD64 architecture. It was an obvious upgrade to x86, so it would clearly do better in the market than IA-64. One of the best aspects of the Opteron was it also happened to be a fantastic 32-bit CPU in addition to AMD64. This was a period where a lot of software, even FOSS wasn't 64-bit clean. There was a lot of pointer arithmetic hiding deep in libraries that were assuming pointers would always be 32-bits. The Opteron running a 32-bit OS at least as well as a 32-bit Athlon was a huge point in its favor. So your existing system running on new Opteron hardware ran fine and you could mix and match Xeon and Opterons in a fleet. Then switch over to 64-bit on the Opterons for (hopefully) better performance.
acdha 4y ago
One thing to remember is that FP performance with well-scheduled code was by far its strongest performing area, and Intel put a lot of work into tuning their compiler for those specific tests. The problem was that it fell off heavily the less your code is like that, especially for the branchy code most business apps depend on. The other big problem was that the x86 compatibility story was worse than the earlier hopes. That meant that it not only wasn’t competitive with the current generation competition but often even the previous or worse - note losing to the original Pentium or even a 486 here: https://tweakers.net/reviews/204/8/intel-itanium-sneak-preview-benchmarks-rc5-chess-en-stream.html https://tweakers.net/reviews/204/8/intel-itanium-sneak-previ... Now, they could have improved that but statistically nobody was going to pay considerably more for lower performance in the hopes that a future update would improve matters. The Athlon and Opteron weren’t just fast, they also had flawless 32-bit support so even if your 64-bit software update never happened you could justify the purchase based on their price/performance.

giantrobot 4y ago

> AMD killed that plan by releasing AMD64 architecture. It was an obvious upgrade to x86, so it would clearly do better in the market than IA-64. One of the best aspects of the Opteron was it also happened to be a fantastic 32-bit CPU in addition to AMD64. This was a period where a lot of software, even FOSS wasn't 64-bit clean. There was a lot of pointer arithmetic hiding deep in libraries that were assuming pointers would always be 32-bits. The Opteron running a 32-bit OS at least as well as a 32-bit Athlon was a huge point in its favor. So your existing system running on new Opteron hardware ran fine and you could mix and match Xeon and Opterons in a fleet. Then switch over to 64-bit on the Opterons for (hopefully) better performance.

acdha 4y ago

One thing to remember is that FP performance with well-scheduled code was by far its strongest performing area, and Intel put a lot of work into tuning their compiler for those specific tests. The problem was that it fell off heavily the less your code is like that, especially for the branchy code most business apps depend on. The other big problem was that the x86 compatibility story was worse than the earlier hopes. That meant that it not only wasn’t competitive with the current generation competition but often even the previous or worse - note losing to the original Pentium or even a 486 here: https://tweakers.net/reviews/204/8/intel-itanium-sneak-preview-benchmarks-rc5-chess-en-stream.html https://tweakers.net/reviews/204/8/intel-itanium-sneak-previ... Now, they could have improved that but statistically nobody was going to pay considerably more for lower performance in the hopes that a future update would improve matters. The Athlon and Opteron weren’t just fast, they also had flawless 32-bit support so even if your 64-bit software update never happened you could justify the purchase based on their price/performance.