Re: [Xen-devel] [PATCH 1/2] cpufreq, powernow: enable/disable core performance boost for all cpus in policy

[Jacob Shin <jacob.shin@xxxxxxx>]

On Thu, Jun 20, 2013 at 08:54:00AM +0100, Jan Beulich wrote:
> >>> On 20.06.13 at 01:07, Jacob Shin <jacob.shin@xxxxxxx> wrote:
> > On Wed, Jun 19, 2013 at 03:14:46PM -0500, Jacob Shin wrote:
> >> Currently, enable/disable turbo mode on AMD is broken:
> >> 
> >> $ xenpm enable-turbo-mode 0 <-- works and proper CPU MSR bit is set
> >> $ xenpm enable-turbo-mode 1 <-- silently broken, MSR bit not set
> >> 
> >> Since ->turbo is per policy, when user requests to enable/disable
> >> turbo mode, we need to set the bit in all of the ->cpus that this
> >> policy affects.
> > 
> > Sorry, I'll have to re-do this [PATCH 1/2], as it does not solve the
> > problem on platforms with a separate policy per CPU.
> 
> But isn't a separate policy per CPU meaning that indeed you want
> to only fiddle with the one CPU that the policy is getting changed
> for?

Yes, this is okay if the end user realizes that on current AMD parts,
disabling turbo on one core means that it affects all other sibling
cores that are on the same node.

$ xenpm disable-turbo-mode 0 </-- hardware bit gets set on CPU0
$ xenpm get-cpufreq-para
...
CPU0
turbo mode: disabled
...
CPU1
turbo mode: enabled

But since CPU0 and CPU1 are in the same Node, in reality CPU1 also in
affect has turbo mode disabled.

If this is okay, then I think the above patch will be fine.

> 
> > 1. We'll have to either globally enable/disable boost for all CPUs, or
> 
> That's clearly not a good path, as the interface is specifically
> intending to allow per-policy control.

Okay.

> 
> > 2. [if there is a easy way to do so] find all Node siblings and set
> > their bits and policy->turbo as well.
> 
> That would be the way to go, pending clarification on the above.

Let me know what you think about my blurb above.

Thanks!


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