Linux and the Desktop Pentium M: Uncommon Performance

The Test

The goal today is to benchmark our newest Pentium M Dothans of both the 400MHz and 533MHz front side bus. We would like to see how these processors compare to the better-performing Athlon 64 and Pentium 4 processors available today, particularly for the same price category. We will also look at how the higher clocked front side bus speed, different memory speeds and different compilers affect our benchmark results.

Performance Test Configuration
Processor(s):	AMD Athlon FX-53 (130nm, 2.4GHz, 1MB L2 Cache, Socket 939) AMD Athlon 64 3800+ (130nm, 2.4GHz, 512KB L2 Cache) AMD Athlon 64 3500+ (130nm, 2.2GHz, 512KB L2 Cache) AMD Athlon 64 3200+ (90nm, 2.0GHz, 512KB L2 Cache) Intel Pentium 4 Extreme Edition 3.4GHz (130nm, 512KB L2 Cache, 2MB L3 Cache) Intel Pentium 4 560 3.6GHz (90nm, 1MB L2 Cache) Intel Pentium M 765 2.1GHz (90nm, 2MB L2 Cache, 533FSB) Intel Pentium M 755 2.0GHz (90nm, 2MB L2 Cache, 400FSB)
RAM:	2 x 512MB Mushkin PC-3200 CL2 (400MHz) 2 x 512MB Corsair PC2-5400 CL3 (475MHz)
Motherboards:	DFI LanParty 915P-T12 (Socket 775) MSI K8T Neo2 (Socket 939) DFI 855GME-MFG
Memory Timings:	Default
Operating System(s):	SuSE 9.1 Professional Kernel 2.6.5-7.108
Compiler:	dave:~ # gcc - v Reading specs from /opt/gcc-mainline/lib/gcc/i586-suse-linux/3.4.1/specs Configured with: ../configure - enable-threads=posix - prefix=/opt/gcc-mainline - with-local-prefix=/usr/local - infodir=/opt/gcc-mainline/share/info - mandir=/opt/gcc-mainline/share/man - libdir=/opt/gcc-mainline/lib - libexecdir=/opt/gcc-mainline/lib - enable-languages=c,c++,f77,objc,java,ada - enable-checking - enable-libgcj - with-gxx-include-dir=/opt/gcc-mainline/include/g++ --with-slibdir=/lib - with-system-zlib - enable-shared --enable-__cxa_atexit i586-suse-linux Thread model: posix gcc version 3.4.1 20040508 (prerelease) (SuSE Linux)
Intel Compiler:	dave:/opt/intel_cc_80/bin # ./icc -v Version 8.1

As you will see from the specifications above, we are recycling most of our benchmarks from the last Linux CPU roundup that we published a few months ago. The two newcomers to the benchmark are the 2.1GHz 533FSB Dothan Pentium M and the 2.0GHz 400FSB Dothan Pentium M. Both processors use the desktop configuration, Socket 479. Socket 479 processors are somewhat difficult to find right now, although they similarly reflect the performance of their Socket 478 counterparts. Unfortunately, the Dothan/Banias Socket 478 pinout is different electrically than the typical desktop Socket 478, and thus you will need to use a Socket 479 board with a Socket 479 Dothan if you plan on using any of these Pentium M's in your desktop anytime soon.

Click to enlarge.

Looking at the CPU proc information we can discern the following:

dave:~/bench/gcc/linux-2.6.4 # cat /proc/cpuinfo 
processor       : 0
vendor_id       : GenuineIntel
cpu family      : 6
model           : 13
model name      : Intel(R) Pentium(R) M processor 2.10GHz
stepping        : 6
cpu MHz         : 2104.892
cache size      : 64 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 2
wp              : yes
flags           : fpu vme de pse tsc msr mce cx8 sep mtrr pge mca cmov pat clflush
                  dts acpi mmx fxsr sse sse2 ss tm pbe tm2 est
bogomips        : 4177.92

The bogomips score seems fairly accurate; the 3.6GHz Nocona reports about 7200BMIPS per physical processor. However, note that there are no SSE3 enhancements, HyperThreading or EM64T addressing capability. All desktop Pentium M processors today are derived from the blade server market and their feature sets reflects that - blade servers are designed to be small, fast and cool; putting 8GB of memory in a blade would not make a lot of sense.

As you can also see from the information above, our Dothan 2.1GHz is in the 6^th stepping, "F". The processor utilizes 64K of L1 cache and 2MB of L2 cache. The DFI motherboard that we use in this analysis keeps our Dothan bus at 100MHz while pushing the clock multiplier up to 21X; thus, effectively running it at 2.1GHz with 400MHz FSB. During the test, we also clock the bus at 133MHz and run the multiplier at 16X, which effectively runs our CPU at 2133MHz with the full 533FSB. This also skews our memory clock a bit - in the first 400MHz configuration, we are running DDR333 (100MHz with a 5:3 ratio). In the second configuration, we use 133MHz at a 4:3 ratio. This is perfectly normal behavior, although keep in mind that the default configuration with our set up runs at DDR200 with the 400MHz FSB. Keep in mind also that we anticipate these lower memory clocks to pinch the Dothan's performance in the long run.