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Pentium 4 Under Linux
A reader writes "I just ran across this article over at LinuxHardware.org that reviews the Pentium 4 under Linux. It gives a lot of insite as to why anyone would want to buy a Pentium 4 and has some great clips from Alan Cox and Jan Hubicka (from the GCC team). Very thorough job."
As Ace's Hardware discovered, the best way to optimize is to use Intel's latest beta compiler. But you can't use this compiler to compile Linux, because Linux uses gcc-specific extensions to C that the Intel compiler does not support.
The Pentium 4 has several glaring faults that cripple it.
the level 1 cache is way too small
it can only pass the decoded micro-ops to 3 of its internal execution units per clock, so it can only execute 3 micro-ops per clock (compare to the Athlon, with up to 9 micro-ops executed per clock)
instructions that execute very quickly on other Pentium chips now execute slowly (in particular, anything involving bit-shifting)
These faults and more are discussed here.
Unlike the Pentium 4, the Athlon executes exisiting x86 code very quickly. You don't need fancy optimization tricks to get code to run fast on an Athlon; it has no major faults to work around.
A Pentium 4 system, with its expensive high-speed RDRAM, will be very fast for certain uses. And it has the lead in raw clock speed. If Intel can crank the clock speed way up, say to double what AMD can do, it won't matter that the Pentium 4 is broken; it will still be the fastest chip you can get. I predict this will not happen; AMD will continue to make ever-faster Athlon chips, which will remain competitive with anything Intel can make. (And of course if you look at the performance-over-price ratio, the AMD chips totally crush the Intel chips.)
Of course, it must be said that the chips are so fast these days that few people will really notice any difference between a good AMD system and a good Intel system. The AMD may out-benchmark the P4, but if both of them can run Quake 3 nice and fast, few people will actually care about the differences.
steveha
lf(1): it's like ls(1) but sorts filenames by extension, tersely
This is so wrong. The AMD core breaks up an x86 instruction into RISC-like "micro-ops" or ROPs, and then various RISC-like execution units go to work executing the ROPs. Up to 9 ROPs can be executed at the same time! This is why the Athlon so thoroughly stomps all over the Intel chips at equivalent clock rates--the AMD chips can get more done per clock. This is especially true for floating point, where the Athlon can execute 3 floating point instructions at once.
Full details here in the AnandTech article. I linked to page 8, the one that has the discussion of how instructions get executed.
This is the reason why Pentiums cost more than AMD's
Total nonsense. Intel chips cost more because Intel charges more. The Pentium 4 is expensive because its die size is freaking huge.
Let's just say I have inside knowledge of Intel products. :-)
You don't seem to know very much about AMD products.
steveha
lf(1): it's like ls(1) but sorts filenames by extension, tersely
The P4 has all the 3d optimizations, just like the old p3's. The only thing is, most of the programs (not all, but most) that depend on those optimizations and dont use athlon optimizations are originally designed as wintel programs, like quake 3. Those programs are also available as binary only, not source. While the P4 is apparently a great system for an avid gamer, for developers the AMD line will probably remain cheaper and more useful to *nix developers like myself.
I am !amused.
for even more insite, try learning to spell.
Treatment, not tyranny. End the drug war and free our American POWs.
Treatment, not tyranny. End the drug war and free our American POWs.
See my user info for links.
I assume http://www.linuxhardware.org%3C/a means http://www.linuxhardware.org ;)
chris@xanadu:~$ whatis /.
/.: nothing appropriate.
It seems to me that the P4/Athlon debate has brought out a lot of bashing of the P4, as it benchmarks slower than comparable or even slower Athlon CPU's.
These same people, however, don't seem to be bashing the GeForce 3, which in many cases benchmarks slower than some GeForce 2 ultra cards. Sure, it's OK for a video card to change its architecture but not the CPU????
People seem to understand that eventually the GF3 will be the card to get IF games are written to that architectures. The same could be said of the P4 IF APPS are written to the new architecture.
Praying for the end of your wide-awake nightmare.
What, me worry?
Somebody needs to work on an ispell module for slashcode; in theory it shouldn't be that difficult. Put computers to work for you. Everybody would be happier, and would look smarter to boot!
Looks like the P4 goes pretty much as fast as anything else unless they turn on the chip specific optimisations, but I don't think that will matter at all, since the average PC purchaser will look at the 2Ghz(ish) ratings and go "Ohmygod - must be weelly fast!" I'm suprised they didn't have a 40 stage pipeline and really get people excited.
I wonder if they'll consider on-board 802.11b when they hit 2.5Ghz?
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If any gcc hackers out there are reading, just le me know where to start poking and I'll try and implement a solution.
Ryan T. Sammartino
Ryan T. Sammartino
"Ancora imparo"