linux-kernel - Re: [PATCH V2 5/6] x86/intel_rdt: Use perf infrastructure for measurements

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Date:   Thu, 6 Sep 2018 13:05:05 -0700
From:   Reinette Chatre <reinette.chatre@...el.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     tglx@...utronix.de, fenghua.yu@...el.com, tony.luck@...el.com,
        mingo@...hat.com, acme@...nel.org, vikas.shivappa@...ux.intel.com,
        gavin.hindman@...el.com, jithu.joseph@...el.com,
        dave.hansen@...el.com, hpa@...or.com, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 5/6] x86/intel_rdt: Use perf infrastructure for
 measurements

Hi Peter,

On 9/6/2018 12:44 PM, Peter Zijlstra wrote:
> On Thu, Sep 06, 2018 at 12:21:59PM -0700, Reinette Chatre wrote:
>> If you do have suggestions on how I can improve the implementation while
>> maintaining (or improving) the accuracy of the measurements I would
>> greatly appreciate it.
> 
> You can reduce the code duplication by using __always_inline functions
> with const function arguments.
> 

Could you please elaborate? I am unable to see how that would help in,
for example:

          if (need_l2) {
                   rdpmcl(l2_hit_pmcnum, l2_hits_after);
                   rdpmcl(l2_miss_pmcnum, l2_miss_after);
          }
          if (need_l3) {
                   rdpmcl(l3_hit_pmcnum, l3_hits_after);
                   rdpmcl(l3_miss_pmcnum, l3_miss_after);
          }

Two issues with the above are:
- the measurements captured in l2_hits_after and l2_miss_after would
include the hits/misses associated with the "if (need_l2)" test
- the measurements captured in l3_hits_after and l3_miss_after would
include the hits/misses associated with both the "if (need_l2)" and "if
(need_l3)" tests.

When I separate the above into the two functions it just becomes either:
                   rdpmcl(l2_hit_pmcnum, l2_hits_after);
                   rdpmcl(l2_miss_pmcnum, l2_miss_after);
or:
                   rdpmcl(l3_hit_pmcnum, l3_hits_after);
                   rdpmcl(l3_miss_pmcnum, l3_miss_after);

Reinette