Introduction

Dothan is something that both perplexes and intrigues us at the same time. Not quite a Pentium 3, not quite a Pentium 4, and not quite something that is entirely different either. Meanwhile, the NetBurst architecture has come under serious strain over the last few years, particularly since Intel's Prescott launch. Is Intel still capable of killer products? And more importantly, do they still dominate on Linux?

As many who follow our Windows reviews know, Pentium M on the desktop is something a few years in the making. Even when the original 130nm Banias processor showed up in 2003, reviewers and customers alike were astonished with the technology. Intel received even more praise when their 90nm Dothan chips of the same product line showed up - utilizing less than 30W during peak operation and less than 5W on idle. Most of these advancements were due to Intel's controversial strategy to rethink the P6 architecture and refining a particularly interesting technology called Enhanced Speed Step. Enhanced Speed Step, also known as EIST, gives the operating system the ability to dynamically clock the processor. Typically, Windows will dedicate the full 100% of the Dothan's clock during intensive operation, but throttle the processor as far down as 10% of its capable speed when the computer is just idling. Thus, Pentium M has achieved incredible status among overclockers and HTPC enthusiasts - on Windows. Today, we will briefly explore the versatility of Pentium M on the Linux desktop. Lessons learned should also apply to the notebook market as well.

That being said, there are already a few fundamental flaws with the Pentium M architecture on Linux, the largest of these being compiler optimizations. While Opteron/Athlon 64 and Pentium M share substantial optimizations from every corner of the OSS universe, Pentium M receives very little regular attention. Dothan/Banias are slightly cursed, since most Linux OSes are built on the - mtune=i686 flag, which specifically tunes compilation to the P6 core (Pentium Pro), from which the Pentium M is derived. Why is that a curse and not a blessing? Although Dothan and Banias certainly share some key elements with the P6 architecture, they are far from it. Pentium M's Micro Ops Fusion, local branch prediction and general optimizations across integer division and register access are completely ignored by the compiler, even when setting - march=pentium-m, since most compilers (particularly anything before GCC 3.4.2) tend to just categorize Pentium M as a P6 processor with a higher clock.

Of course, the Intel C compiler, ICC, behaves very differently, but unfortunately, isn't very free either. We have a few tests today that include the non-commercial ICC as well and we see how they stack up against GCC 3.4.1. So, if it doesn't bother you that the majority of Linux sees your new Pentium M as a glorified Pentium Pro, without further ado, let's check out how it actually performs against other processors that we have looked at in the past.

The Test
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  • Adul - Friday, December 24, 2004 - link

    stephenbrooks "superlinearly" even a word? Though I do understand what you mean. Reply
  • KristopherKubicki - Friday, December 24, 2004 - link

    abakshi: Intel roadmaps say only DDR1 for 915GL.

    Kristopher
    Reply
  • stephenbrooks - Friday, December 24, 2004 - link

    The Pentium M scales superlinearly with frequency in a few of the time vs. clock-speed benches (and I'm not talking about the 400->533 FSB improvement), which is pretty interesting. I wouldn't have expected a chip like this to get more efficient at _higher_ clocks. Reply
  • abakshi - Friday, December 24, 2004 - link

    Well FSB533 is here, but 800 would be a more significant move with Dothan. A P-M with FSB800, even DDR400 let's say (rather than the DDR2 that should be supported by using a 915 northbridge), and higher clockspeeds - maybe about 2.4-2.6 Ghz - would be amazing.

    Linux performance will of course depend on other factors such as those mentioned in the article, but the performance under Windows of even the FSB400 2.0 Dothan is awesome -- when overclocked to 2.4Ghz, it's able to keep up with, and at times beat, the latest P4 Prescott and EE's, and A64's, for tasks like gaming:

    http://www.gamepc.com/labs/view_content.asp?id=dot...

    http://translate.google.com/translate?hl=en&sl...
    Reply
  • Lonyo - Friday, December 24, 2004 - link

    If Intel gave it a FSB and memory speed boost (ie: 533MHz or 800MHz FSB) and DDR533+, then Dothan could really be something.
    With Intels talk of dual core processors, a dual core Dothan, with its low heat output, would be awesome (but costly with 2MB of cache).
    2x30w = 60w = less than Prescott.

    It looks promising, if only Intel would bring it to the affordable desktop :(
    Reply
  • VortigernRed - Friday, December 24, 2004 - link

    "Although it holds up well against an Athlon 64 3200+,"

    Although the Dothan looks to be a superb chip you are certainly overstating its performance here, this is comment is WRT the Shake benchmarks and, effectively, the A64 3200 is twice as fast as the dothan. This would be like saying, for example, a R9800XT holds up well against an X800XT or an AXP2200+ holds up well against a A64 3800+ :-)

    Also whilst the DDR400 does improve performance it can't help the Dothan where it is really far behind, the kernel compile benchmarks, for instance, it is still 3x slower than any of the other chips on the chart.

    Dothan (or really its derivatives) have loads of potential to compete with the A64 on all fronts (Performance, power, heat, with Intels manufacturing, even cost) given enough effort by Intel (which I'm sure they are doing). I can hardly wait to see widespread adoption on the desktop and, frankly, to see the back of the P4. A desktop Celeron PM (1MB l2, lower FSB) could be the new overclocking king.
    Reply
  • bersl2 - Friday, December 24, 2004 - link

    You might want to ask on the GCC mailing lists (http://gcc.gnu.org/lists.html) about --march=pentium-m. Reply

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