linux-kernel - Re: [PATCH V1 10/13] selftests/resctrl: Change Cache Allocation Technology (CAT) test

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Date:   Wed, 11 Mar 2020 13:55:12 -0700
From:   Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
To:     Reinette Chatre <reinette.chatre@...el.com>, shuah@...nel.org,
        linux-kselftest@...r.kernel.org
Cc:     tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        tony.luck@...el.com, babu.moger@....com, james.morse@....com,
        ravi.v.shankar@...el.com, fenghua.yu@...el.com, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH V1 10/13] selftests/resctrl: Change Cache Allocation
 Technology (CAT) test

Hi Reinette,

On Wed, 2020-03-11 at 13:22 -0700, Reinette Chatre wrote:
> Hi Sai,
> 
> On 3/11/2020 12:14 PM, Sai Praneeth Prakhya wrote:
> > On Wed, 2020-03-11 at 10:03 -0700, Reinette Chatre wrote:
> > > On 3/10/2020 6:59 PM, Sai Praneeth Prakhya wrote:
> > > > On Tue, 2020-03-10 at 15:14 -0700, Reinette Chatre wrote:
> > > > > Hi Sai,
> > > > > 

[SNIP]

> > > > Please let me know if you think otherwise
> > > 
> > > I think this patch can be split up into logical changes without breaking
> > > the tests along the way. In my original review I identified two changes
> > > that can be split out. Other things that can be split out:
> > > - have CAT test take shareable bits into account
> > > - enable measurement of cache references (addition of this new perf
> > > event attribute, hooks to get measurements, etc.)
> > > - transition CAT test to use "perf rate" measurement instead of "perf
> > > count"
> > > - etc.
> > 
> > I think we could split the patch like this but I am unable to see the
> > benefit
> > of doing so.. (Sorry! if I misunderstood what you meant).
> 
> Separating patches into logical changes facilitates review. Please
> consider this huge patch from the reviewer's perspective - it consists
> out of many different changes and is hard to review. If instead this
> patch was split into logical changes it would make it easier to
> understand what it is trying to do/change.

Ok.. makes sense.

> This is not a request that I invent but part of the established kernel
> development process. Please see
> Documentation/process/submitting-patches.rst (section is titled "Separate
>  your changes").

Sure! will take a look at it.

> 
> > As CAT and CQM test cases are buggy (CAT is not testing CAT at all) and we
> > are
> > not attempting to fix them by incremental changes but completely changing
> > the
> > test plan itself (i.e. the way the test works), so why not just remove
> > older
> > test cases and add new test? I thought this might be more easier for
> > review
> > i.e. to see the new test case all at once. Don't you think so?
> 
> From what I understand the new test continues to use many parts of the
> original test. Completely removing the original test would thus end up
> needing to add back a lot of code that was removed. Incremental changes
> do seem appropriate to me. The logical changes I listed above actually
> has nothing to do with "the way the test works". When those building
> blocks are in place the test can be changed in one patch and it would be
> much more obvious how the new test is different from the original.

Ok.. makes sense. Will split the patch as you suggested.

Regards,
Sai