Re: [dpdk-dev] [0/9] examples/vm_power: 100% Busy Polling

["Hunt, David" <david.hunt@intel.com>]

Hi Thomas,

On 12/7/2018 8:09 PM, Thomas Monjalon wrote:
> 26/06/2018 11:23, David Hunt:
>> This patch set adds the capability to do out-of-band power
>> monitoring on a system. It uses a thread to monitor the branch
>> counters in the targeted cores, and calculates the branch ratio
>> if the running code.
>>
>> If the branch ratop is low (0.01), then
>> the code is most likely running in a tight poll loop and doing
>> nothing, i.e. receiving no packets. In this case we scale down
>> the frequency of that core.
>>
>> If the branch ratio is higher (>0.01), then it is likely that
>> the code is receiving and processing packets. In this case, we
>> scale up the frequency of that core.
>>
>> The cpu counters are read via /dev/cpu/x/msr, so requires the
>> msr kernel module to be loaded. Because this method is used,
>> the patch set is implemented with one file for x86 systems, and
>> another for non-x86 systems, with conditional compilation in
>> the Makefile. The non-x86 functions are stubs, and do not
>> currently implement any functionality.
>>
>> The vm_power_manager app has been modified to take a new parameter
>>     --core-list or -l
>> which takes a list of cores in a comma-separated list format,
>> e.g. 1,3,5-7,9, which resolvest to a core list of 1,3,5,6,7,9
>> These cores will then be enabled for oob monitoring. When the
>> OOB monitoring thread starts, it reads the branch hits/miss
>> counters of each monitored core, and scales up/down accordingly.
> It looks to be a feature which could be integrated in DPDK libs.
> Why choosing to implement it fully in an example?

I needed to set up a thread that looped tightly (~100uS interval) and 
run it on it's
own core. From what I have seen in other cases, it is usually the 
application that
allocates cores and decides what to run on them. I did think about putting
some of it in a library, but for this case I thought it made more sense 
to keep
it purely as a sample app.

Regards,
Dave.