Phenom II X6 Performance Under Linux Below Expectations

May 03, 2010

In testing the Phenom II X6, Linux Magazine noticed that AMDs new processor doesn't have the full performance under the current Linux kernel. A bug in Linux power management throws a wrench into the six-core processing.

With Ubuntu 9.04 and kernel 2.6.28, the Phenom II X6 1090T processor exhibited 19% better performance, much like Intel's "Gulftown" Core i7 980, in the LUbench benchmark. However, the performance was far more disappointing with Ubuntu 9.10 under kernel 2.6.31. Only by deactivating AMD's Cool'n'Quiet power-saving technology did the Phenom II X6 get anywhere near the expected performance with Ubuntu 9.10.

AMD's Operating Systems Research Center (OSRC) in Dresden, responsible for Linux development under the direction of Chris Schlaeger, confirmed that the new Turbocore mode of the Phenom II X6 was getting into conflict with the kernel's powernow-k8 frequency regulator module. The module falsely assumes the turbo clock as the maximum frequency. But because only the CPU itself can do the overclocking, this leads to a Turbocore knockout. Even a reduction to miminum clocking is impossible. The problem affects all AMD CPUs with the Turbocore feature under kernel 2.6.30 and later. The only available CPUs with Turbocore right now are the Phenom II X6 1055T and 1090T.

AMD has already sent a relevant patch upstream. The chipmaker is encouraging distro maintainers to update with this patch as soon as possible. The patch should be included in the next Ubuntu 10.04 kernel update. To determine if the issue affects your system, use the following command:

dmesg | grep "pstate 0"

Alternatively, use a widget or applet that shows all available processor clock rates.

If the maximum frequency (pstate 0) is shown as 3600 MHz for the 1090T or 3300 MHz for the 1055T, the system's performance is reduced.

Until the patch is available, Linux users should deactivate Cool'n'Quiet in the BIOS, or blacklist the powernow-k8 kernel module (the latter seems a better solution if Windows is also installed).In our tests, the power use is only 17 watts higher when idling, at least under the unaffected kernel in Ubuntu 9.04. No difference was measured under heavy load, whether it was with one core or all six.

Related content

  • Phenomenon Redux: AMD Phenom II in Linux Test

    A recent Linux Community test compared the AMD Phenom X4 with a Turion X2 and Intel P9400. Meanwhile AMD has sent us its new Phenom II processor, prompting a new test. These are the latest benchmark results.

  • A Little Overclocking: Record Set for Phenom II under Linux

    For real overclocking you need liquid nitrogen and helium. All you need to do in winter is open your window.

  • KSplice

    Uptime is often just as important as updates. But doesn't a kernel patch require a reboot? Ksplice lets you have your cake and eat it too.

  • First Look at Gnome 3

    The new Gnome desktop offers a simpler work environment – once you become accustomed to the new navigation tools.

  • Kernel Tips

    Worried about a recent security exploit? Want to take advantage of a new hardware feature? You don’t need to be a Linux expert to patch and compile the Linux kernel. We'll show you how to get started.

comments powered by Disqus

Issue 23: Raspberry Pi Adventures/Special Editions

Buy this issue as a PDF

Digital Issue: Price $15.99
(incl. VAT)


njobs Europe
Njobs Netherlands Njobs Deutschland Njobs United Kingdom Njobs Italia Njobs France Njobs Espana Njobs Poland
Njobs Austria Njobs Denmark Njobs Belgium Njobs Czech Republic Njobs Mexico Njobs India Njobs Colombia