Re: [PATCH v7 3/4] perf,x86: add Intel RAPL PMU support

[Stephane Eranian]

On Wed, Nov 27, 2013 at 7:35 PM, Vince Weaver <vince@xxxxxxxxxx> wrote:
> On Tue, 12 Nov 2013, Stephane Eranian wrote:
>
>> This patch adds a new uncore PMU to expose the Intel
>> RAPL energy consumption counters. Up to 3 counters,
>> each counting a particular RAPL event are exposed.
>>
>> The RAPL counters are available on Intel SandyBridge,
>> IvyBridge, Haswell. The server skus add a 3rd counter.
>
> So I notice PP1 (which is the GPU power on non-server chips)
> is not supported.
>
> Is that just for simplicity?
>
Does it work on specific models only? I bet so. How to detect those?

>> The following events are available and exposed in sysfs:
>> - power/energy-cores: power consumption of all cores on socket
>> - power/energy-pkg: power consumption of all cores + LLc cache
>> - power/energy-dram: power consumption of DRAM (servers only)
>
> This "power" naming seems a bit generic.  If other hardware has power
> measurements can they be put in the same directory?
> power/gpu? power/usb?
>
I think so.

> Also, can support for reading the power from other vendors be put here?
> Like AMDs (unfortunately named) APM (active power management) power
> readings?
>
>> Files are:
>>       /sys/devices/power/events/energy-*.unit
>>       /sys/devices/power/events/energy-*.scale
>
> Are all of these sys files having documentation added under
> Documentation/ABI?
>
Not yet.

>> The RAPL PMU is uncore by nature and is implemented such
>> that it only works in system-wide mode. Measuring only
>> one CPU per socket is sufficient. The /sys/devices/power/cpumask
>> file can be used by tools to figure out which CPUs to monitor
>> by default. For instance, on a 2-socket system, 2 CPUs
>> (one on each socket) will be shown.
>
> do the measurements require CAP_SYS_ADMIN like other system-wide uncore
> measurements?  It didn't look like it in the patch but I might have missed
> it.
>
Measurements are limited to system-wide counting. Thus, you need
CAP_SYS_ADMIN.

> I'm sure the security people will start making claims that you can make
> guesses about password encryption algorithms based on the global power
> consumption numbers.
>
>
> Sorry if these are annoying questions, I am glad to see this driver make
> progress, as I've had the misfortune of maintaining various user-space-MSR
> hacks designed to get this info because of lack of kernel support.
>
You don't really need a driver, you can also just use modprobe msr + the
turbostat utility now part of the kernel source tree. It taps into the same
counters.
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