Linux and L2 Cache; Sempron vs. Athlon
by Kristopher Kubicki on August 18, 2004 2:29 AM EST- Posted in
- Linux
Conclusions
The first conclusion we came to without even really running any benchmarks. Primarily, the lack of 64-bit addressing on the Sempron 3100+ probably makes a bit of sense; the A64 2800+ and the Sempron 3100+ are both budget oriented processors - it is very unlikely anyone will utilize more than 4GB of memory on either processor. The real payoff of the Athlon 64 processors (the onboard memory controller) is found on both the Sempron and Athlon 64.
We also noted in our analysis that the Sempron 3100+ scored very similar performance marks to the Athlon 64 2800+; and it should. Both processors utilize 1.8GHz clock speeds and 130nm production, but the Sempron 3100+ only runs on half the L2 cache of the 2800+. Again, the only major functional differences we noticed between the two processors was the lack of 64-bit operation (with a few exceptions). That being said, at least on Linux, we cannot vouche for AMD's PR rating since the Athlon 64 3000+ lead the Sempron 3100+ in every single benchmark. AMD states the PR rating only compares the Sempron to the Celeron product line, but since Intel dropped the GHz rating on the Celeron chips months ago, that seems like a moot point.
On a cost analysis, the Sempron 3100+ packs a lot of punch for $130. We lose 64-bit addressing and the additional cache for $20 when compared to an Athlon 64 2800+, but as we saw in our benchmarks the cache only provided significant advantages on database and encoding applications - not something most people generally use a budget CPU for anyway. If you're looking to limit yourself to 32-bit computing on the Linux desktop, the Sempron 3100+ cannot keep up with an Athlon 64 3000+ or even a 2800+. However, the 10% cost savings between the 2800+ and the 3100+ is much better than the 2 to 5% decrease in performance we saw between the two processors.
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Matthew Daws - Friday, August 20, 2004 - link
Kris: Oh, okay, sorry, yes, that makes sense. Have you tried the Windows executable yet? I've verified that with TSCP 1.7.3 I'm getting reasonable results, so it seems likely that my results with v1.8.1 are not too far off base...--Matt
KristopherKubicki - Friday, August 20, 2004 - link
Rys:Correct, but that doesnt mean it still does not lack 64-bit addressing ;) And in reality, how critical would any desktop CPU today need to address more than 48bits ? Isnt that something like 1TB?
Kristopher
KristopherKubicki - Friday, August 20, 2004 - link
Matthew: I read this:>You shouldn't see any difference with linux:
>indeed, only a linux box I have access to, with GCC
>3.2.2 (I *think* it's a P4 2.8GHz, but I'm not 100%
>sure: I'm doing a remote-login right now, so cannot
>check!) I get 365K with (-O3 -march=pentium4).
So your 2.8C is getting the same marks as my 3.6 nocona -- is what i meant.
Kristopher
Rys - Friday, August 20, 2004 - link
You repeatedly mention the Sempron's 'lack of 64-bit addressing'. None of the CPU's on test, including the Athlon 64, can address a 64-bit memory space. All current AMD64 implementations can only address a 40-bit physical address space and a 48-bit virtual address space.Rys
Matthew Daws - Friday, August 20, 2004 - link
Kris,I am confused: in the link you gave me, the Xeon is getting circa 350K, which is way better than I getting, as expected... Okay, so it's low clock for clock, but you said: "Youre getting higher numbers than i got with my Xeon 3.6GHz chip."
--Matt
Matthew Daws - Friday, August 20, 2004 - link
Kris,I've downloaded TSCP 1.7.3 which Tom Kerrigan has collected a lot of benchmarking data about. It also gives a MIPS rating: I get 2136 MIPS (with GCC -O3 -march=pentium4) and 2174 (with the included windows benchmark) These compare well with the data on his website (http://home.comcast.net/~tckerrigan/bench.html) where this puts my 2GHZ Celeron at about the same level an a P4 1800, which seems reasonable for a heavy CPU benchmark.
I suggested that on your test system you run the precompiled Windows executable which Tom gives: this should give an approximate value, as Visual C++ and GCC produce roughly the same performance of code, and with this benchmark, switching between Windows and Linux really shouldn't make a difference. You might also try the earlier code, as I have just done, and then you'll have a 3rd party (namely Tom's list) to compare against...
--Matt
Wesley Fink - Friday, August 20, 2004 - link
#32 - I would think the CPU scaling charts in Doom 3 at http://www.anandtech.com/cpuchipsets/showdoc.aspx?... would be all the proof you need to see the 3100+ is the better value. The 3100+ is 75.3FPS, the XP 3200+ is 68FPS, and the 2500+ is 55.6FPS.If DX9 game performance is not convincing, then you might refresh your memory in pages and pages of benchmarks comparing the 3100+ 754 and 2500+ Socket A in http://www.anandtech.com/cpuchipsets/showdoc.aspx?...
thornc - Friday, August 20, 2004 - link
My main problem with the article is that the Athlon XP 2500+ with Barton core was not included!I am thinking of getting a new system and I intend to use a Barton XP, but if I might change my mind if I see prove that the Sempron is a better deal.
TauCeti - Friday, August 20, 2004 - link
Hi Matthew, Kris and also hello to dougSF30 from siliconinvestor ;)Nice discussion here!
I think there is a way to _really_ understand e.g. the TSCP benchmark scores on all AMD CPUs.
AMD offers (for free) the "AMD CodeAnalyst™ Performance Analyzer for Linux 2.2" and the "AMD Simulation Utilities 2.1"
afaik it is possible with those tools to profile any target code (in this case the TSCP bench) and then even simulate the execution of that code for different CPUs down to assembler code/cache state and even deeper into CPU execution unit usage.
quote from AMD: "The data presented is at the assembly instruction level and is not intended to assist a programmer working in a high-level language. The detailed data on the execution of each instruction takes into account the previous instructions executed and the state of the processor caches. The data is obtained by running the target block of code, then using the debug capabilities of the processor to single step through each opcode to obtain an execution trace. This execution trace is then fed into a Processor Simulation that analyzes the execution."
I think getting used to this tool and knowing how to interpret the results would be very fruitful for any reviewer (and programmer). Dresdenboy at mersenneforum.org used it to dissect the low SSE2 Performance of the AMD64s in the prime95 code.
The downside is that this does not look like an easy task even for a 'normal' experienced programmer. I even don't know if such large code-blocks like TSCPs bench can be used with the tool or if it is only suitable for inner-loop optimization.
Tau
balzi - Friday, August 20, 2004 - link
So I take it by the ignorance that no one really cares if the graphs are readable -- oh well.. I'll still read Anandtech but maybe I won't enjoy it as much in the future.