linux-kernel - Re: [PATCH rcu 3/6] rcu/rcuscale: Move rcu_scale_*() after kfree_scale

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Date:   Thu, 11 May 2023 21:15:17 -0700
From:   Joel Fernandes <joel@...lfernandes.org>
To:     "Zhuo, Qiuxu" <qiuxu.zhuo@...el.com>
Cc:     paulmck@...nel.org, rcu@...r.kernel.org,
        linux-kernel@...r.kernel.org, kernel-team@...a.com,
        rostedt@...dmis.org
Subject: Re: [PATCH rcu 3/6] rcu/rcuscale: Move rcu_scale_*() after kfree_scale_cleanup()



> On May 11, 2023, at 8:20 PM, Zhuo, Qiuxu <qiuxu.zhuo@...el.com> wrote:
> 
> 
>> 
>> From: Paul E. McKenney <paulmck@...nel.org>
>> ...
>>>> I wish diff was better at showing what really changed. The meld tool
>>>> can help but its gui...
>>>> 
>>>> Should I run meld later (I'm out at a conference so no access to
>>>> meld-capable
>>>> machines) or are we sufficiently confident that the lines were moved
>>>> as-is ? :)
>>>> 
>>> 
>>> Thank you, Joel for this concern. Good to know the meld diff GUI tool.
>>> I just run the command below and confirmed that the lines were moved
>>> as-is: rcu_scale_{cleanup,shutdown}() follows kfree_scale_cleanup().
>>> You may double check it ;-).
>>> 
>>>      meld --diff ./rcuscale.c.before ./rcuscale.c.after
>> 
>> Nice, thank you both!
>> 
>> Another option is to check out the commit corresponding to this patch, then
>> do "git blame -M kernel/rcu/rcuscale.c".  Given a move-only commit, there
>> should be no line tagged with this commit's SHA-1.
> 
> Just had a good experiment with the "git blame -M" option: 
> - Used this option to prove a move-only commit quickly (no line tagged with that commit) (the fastest method to me). 
> - Then just only needed to quickly check the positions of the moved code chunk by myself (easy).  
> 
> Thank you, Paul for sharing this. It's very useful to me. 

Looks good to me as well and thank you both for sharing the tips.

 - Joel



> 
>> They say that another option is to use "git diff --color-moved", which colors
>> the changes.  That it does, but I am hard-pressed to work out exactly what
>> distinguishes a moved hunk from an added or removed hunk.
>> Fall colors vs. winter colors?  Exterior vs. interior?  Any particular decade in
>> the endless rush of changes to fashion?  Perhaps someone with normal color
>> vision (to say nothing of better fashion sense) could try it.
>> 
>> On the other hand: "default: Is a synonym for zebra. This may change to a
>> more sensible mode in the future."  So maybe it is not just me.  ;-)
>> 
>> You can also apparently choose colors using "color.diff.newMoved" and
>> "color.diff.oldMoved" when using "--color-moved=plain".
>> 
>> But "git diff --color-moved=dimmed-zebra" might be more to the point for
>> someone like me.  I would need to experiment with it more in order to
>> confirm my hypotheses about what it is doing.  To say nothing of building
> 
> Yup, this looks a bit painful for me too (need experiments to confirm hypotheses ...). 
> 
>> trust in it.  Plus I have to open a color terminal to use it effectively.
>> So maybe "git blame -M" continues to be the tool for me?
>> 
>>                            Thanx, Paul