Re: perf/x86/intel/uncore: propose to support IIO free-running counters in 4.14

["Jin, Yao" <yao.jin@linux.intel.com>]

On 8/28/2018 1:17 PM, Greg KH wrote:
> On Tue, Aug 28, 2018 at 11:11:02AM +0800, Jin, Yao wrote:
>> Hi,
>>
>> The upstream kernel has supported IIO free-running counters on Skylake
>> server. As of Skylake Server, there are a number of free running counters in
>> each IIO Box that collect counts of per-box IO clocks and per-port
>> Input/Output x BW/Utilization.
>>
>> There are three types of IIO free-running counters on Skylake server:
>>
>> 1. IO CLOCKS counter: a clock of IIO box.
>>
>> 2. BANDWIDTH counters: count inbound(PCIe->CPU)/outbound(CPU->PCIe)
>> bandwidth.
>>
>> 3. UTILIZATION counters: count input/output utilization.
>>
>> With these IIO free-running counters, we can get good observation for IIO
>> traffic on Skylake server. For example, we can see the IIO inbound bandwidth
>> (PCIe->CPU).
>>
>> root@skx /sys/devices# perf stat -a -e
>> uncore_iio_free_running_2/bw_in_port0/
>> ^C
>>   Performance counter stats for 'system wide':
>>
>>              153.19 MiB  uncore_iio_free_running_2/bw_in_port0/
>>
>>         8.037701069 seconds time elapsed
>>
>> I propose to backport the patches which support IIO free-running counters to
>> 4.14 stable kernel.
>>
>> perf/x86/intel/uncore: Introduce customized event_read() for client IMC
>> uncore
>> 2da331465f44f9618abe8837d1a68405d550b66e
>>
>> perf/x86/intel/uncore: Add new data structures for free running counters
>> 927b2deb067b8b4753fc09c7a42092f43fc0c1f6
>>
>> perf/x86/intel/uncore: Add infrastructure for free running counters
>> 0e0162dfcd1fbe4c711ee86f24f966c318999603
>>
>> perf/x86/intel/uncore: Support IIO free-running counters on SKX
>> 0f519f0352e37e7d71bdce5559517c74a35f6e33
>>
>> perf/x86/intel/uncore: Expose uncore_pmu_event*() functions
>> 5a6c9d94e9ed7410142bc6fcb638a4db1895aa0c
>>
>> perf/x86/intel/uncore: Clean up client IMC uncore
>> 9aae1780e7e81e54edfb70ba33ead5b0b48be009
> 
> Where in the stable kernel rules does it say that these types of patches
> are ok to be backported?
> 
> Why not just use a newer kernel release if you want to use these new
> features?  What is preventing these users from using 4.18 or newer?
> 
> thanks,
> 
> greg k-h
> 

Hi Greg,

Yes, the stable kernel doesn't contain one rule that it can accept a new 
feature. (https://www.kernel.org/doc/html/v4.15/process/stable-kernel 
rules.html)

While this proposed feature (IIO free-running counters) is useful for 
server users to observe the data traffic between CPU and IO on Skylake 
server. For server customers, we know they prefer to use stable kernels.

The customers may maintain their own branches with the patches. But from 
my personal opinion, it would be better if the official stable kernel 
can support that. That's just my proposal. :)

Thanks
Jin Yao