PowerNow! frequency scaling causes stalls

[spam@altium.nl (Dick Streefland)]

I have a new laptop with an AMD Mobile Sempron, and I'm experimenting
with the PowerNow! frequency scaling. It seems to work, but on every
frequency change, everything stalls for 3-4 seconds, even the X mouse
pointer! Keyboard input seems to be buffered though. Is this normal?

I'm currently using the builtin frequency scaling "governors" of the
kernel with the following settings:

echo ondemand > /sys/devices/system/cpu/cpu0/cpufreq/scaling_governor 
echo 15000000 > /sys/devices/system/cpu/cpu0/cpufreq/ondemand/sampling_rate
echo 1        > /sys/devices/system/cpu/cpu0/cpufreq/ondemand/ignore_nice

However, using the powernow daemon results in the same behavior.

Here are the relevant kernel (2.6.13.2) options:

#
# CPU Frequency scaling
#
CONFIG_CPU_FREQ=y
CONFIG_CPU_FREQ_TABLE=y
CONFIG_CPU_FREQ_DEBUG=y
CONFIG_CPU_FREQ_STAT=y
CONFIG_CPU_FREQ_STAT_DETAILS=y
# CONFIG_CPU_FREQ_DEFAULT_GOV_PERFORMANCE is not set
CONFIG_CPU_FREQ_DEFAULT_GOV_USERSPACE=y
CONFIG_CPU_FREQ_GOV_PERFORMANCE=y
CONFIG_CPU_FREQ_GOV_POWERSAVE=y
CONFIG_CPU_FREQ_GOV_USERSPACE=y
CONFIG_CPU_FREQ_GOV_ONDEMAND=y
CONFIG_CPU_FREQ_GOV_CONSERVATIVE=y

#
# CPUFreq processor drivers
#
CONFIG_X86_ACPI_CPUFREQ=y
# CONFIG_X86_POWERNOW_K6 is not set
# CONFIG_X86_POWERNOW_K7 is not set
CONFIG_X86_POWERNOW_K8=y
CONFIG_X86_POWERNOW_K8_ACPI=y
# CONFIG_X86_GX_SUSPMOD is not set
# CONFIG_X86_SPEEDSTEP_CENTRINO is not set
# CONFIG_X86_SPEEDSTEP_ICH is not set
# CONFIG_X86_SPEEDSTEP_SMI is not set
# CONFIG_X86_P4_CLOCKMOD is not set
# CONFIG_X86_CPUFREQ_NFORCE2 is not set
# CONFIG_X86_LONGRUN is not set
# CONFIG_X86_LONGHAUL is not set

This is reported in /var/log/messages:

Oct  3 22:04:35 acer kernel: CPU: AMD Mobile AMD Sempron(tm) Processor 3000+ stepping 02
[...]
Oct  3 22:04:35 acer kernel: powernow-k8: Found 1 AMD Athlon 64 / Opteron processors (version 1.50.3)
Oct  3 22:04:35 acer kernel: powernow-k8:    0 : fid 0xa (1800 MHz), vid 0xa (1300 mV)
Oct  3 22:04:35 acer kernel: powernow-k8:    1 : fid 0x8 (1600 MHz), vid 0xc (1250 mV)
Oct  3 22:04:35 acer kernel: powernow-k8:    2 : fid 0x0 (800 MHz), vid 0x13 (1075 mV)
Oct  3 22:04:35 acer kernel: cpu_init done, current fid 0xa, vid 0xa

-- 
Dick Streefland                      ////                      Altium BV
dick.streefland@altium.nl           (@ @)          http://www.altium.com
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