linux-kernel - Re: [PATCH v1 4/6] perf threads: Move threads to its own files

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Date: Tue, 27 Feb 2024 22:39:58 -0800
From: Namhyung Kim <namhyung@...nel.org>
To: Ian Rogers <irogers@...gle.com>
Cc: Arnaldo Carvalho de Melo <acme@...nel.org>, Peter Zijlstra <peterz@...radead.org>, 
	Ingo Molnar <mingo@...hat.com>, Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Adrian Hunter <adrian.hunter@...el.com>, Oliver Upton <oliver.upton@...ux.dev>, 
	Yang Jihong <yangjihong1@...wei.com>, linux-kernel@...r.kernel.org, 
	linux-perf-users@...r.kernel.org, bpf@...r.kernel.org
Subject: Re: [PATCH v1 4/6] perf threads: Move threads to its own files

On Tue, Feb 27, 2024 at 1:42 PM Ian Rogers <irogers@...gle.com> wrote:
>
> On Tue, Feb 27, 2024 at 11:17 AM Arnaldo Carvalho de Melo
> <acme@...nel.org> wrote:
> >
> > On Tue, Feb 27, 2024 at 09:31:33AM -0800, Namhyung Kim wrote:
> > > I can see some other differences like machine__findnew_thread()
> > > which I think is due to the locking change.  Maybe we can fix the
> > > problem before moving the code and let the code move simple.
> >
> > I was going to suggest that, agreed.
> >
> > We may start doing a refactoring, then find a bug, at that point we
> > first fix the problem them go back to refactoring.
>
> Sure I do this all the time. Your typical complaint on the v+1 patch
> set is to move the bug fixes to the front of the changes. On the v+2
> patch set the bug fixes get applied but not the rest of the patch
> series, etc.
>
> Here we are refactoring code for an rb-tree implementation of threads
> and worrying about its correctness. There's no indication it's not
> correct, it is largely copy and paste, there is also good evidence in
> the locking disciple it is more correct. The next patch deletes that
> implementation, replacing it with a hash table. Were I not trying to
> break things apart I could squash those 2 patches together, but I've
> tried to do the right thing. Now we're trying to micro correct, break
> apart, etc. a state that gets deleted. A reviewer could equally
> criticise this being 2 changes rather than 1, and the cognitive load
> of having to look at code that gets deleted. At some point it is a
> judgement call, and I think this patch is actually the right size. I
> think what is missing here is some motivation in the commit message to
> the findnew refactoring and so I'll add that.

I'm not against your approach and actually appreciate your effort
to split rb-tree refactoring and hash table introduction.  What I'm
asking is just to separate out the code moving.  I think you can do
whatever you want in the current file.  Once you have the final code
you can move it to its own file exactly the same.  When I look at this
commit, say a few years later, I won't expect a commit that says
moving something to a new file has other changes.

Thanks,
Namhyung