RE: [Xen-devel] Performance difference between Xen versions

["Tian, Kevin" <kevin.tian@xxxxxxxxx>]

> From: John Weekes
> Sent: Tuesday, May 03, 2011 3:16 AM
> 
> On 5/2/2011 11:43 AM, John Weekes wrote:
> >
> > The important thing that I missed on my end was not having the ACPI
> > processor driver selected (for some reason). I had cpufreq and ACPI
> > enabled, but I needed that, as well.
> 
> cpufreq seems to be working now, as is xenpm (and using xenpm is much easier
> than setting the Xen command line), but I'm still not seeing signs that turbo
> mode is bumping up my CPU speed beyond the standard value, as I would
> expect it to.

you won't know the exact frequency bumped up in the turbo mode, as it's all 
handled
by the CPU itself. what xen can do is just to tell the cpu now I'm OK to enter 
turbo 
mode, which is 2268000 (1M higher than normal P0). Then CPU will decide whether
current code can be overclocked based on various conditions, such as TDP, other
core activities in the same package, ...

One possibility to verify that turbo mode does work is to run a CPU intensive 
workload
on one core, while keeping other cores mostly idle. Then choose cpufreq governor
to be performance, and then compare your benchmark when BIOS turbo mode is
on/off. This should give you some feeling whether turbo mode works on your 
platform.

Thanks
Kevin

> 
> Here's what it looks like when I start a single process that spins and gobbles
> down a core:
> 
> # xenpm get-cpufreq-states | grep current
> current frequency    : 1600 MHz
> current frequency    : 1600 MHz
> current frequency    : 1600 MHz
> current frequency    : 1600 MHz
> current frequency    : 1600 MHz
> current frequency    : 2268 MHz
> current frequency    : 1600 MHz
> current frequency    : 1600 MHz
> current frequency    : 1600 MHz
> current frequency    : 1600 MHz
> current frequency    : 1600 MHz
> current frequency    : 1600 MHz
> current frequency    : 1600 MHz
> current frequency    : 1600 MHz
> current frequency    : 1600 MHz
> current frequency    : 1600 MHz
> current frequency    : 1600 MHz
> current frequency    : 1600 MHz
> current frequency    : 1600 MHz
> current frequency    : 1600 MHz
> current frequency    : 1600 MHz
> current frequency    : 1600 MHz
> current frequency    : 1600 MHz
> current frequency    : 1600 MHz
> 
> And looking at the core when running at the higher speed, I see:
> 
> # xenpm get-cpufreq-para 5
> cpu id               : 5
> affected_cpus        : 5
> cpuinfo frequency    : max [2268000] min [1600000] cur [2268000]
> scaling_driver       : acpi-cpufreq
> scaling_avail_gov    : userspace performance powersave ondemand
> current_governor     : ondemand
>    ondemand specific  :
>      sampling_rate    : max [10000000] min [10000] cur [20000]
>      up_threshold     : 80
> scaling_avail_freq   : *2268000 2267000 2133000 2000000 1867000 1733000
> 1600000
> scaling frequency    : max [2268000] min [1600000] cur [2268000]
> turbo mode           : enabled
> 
> Does it do it silently? If so, how can I see the true frequency?
> 
> -John
> 
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