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SubjectRe: [PATCH v3 00/12] perf, persistent: Add persistent events
On Fri, Mar 28, 2014 at 03:54:11PM +0100, Jean Pihet wrote:
> Hi,
>
> Now that the feature is resurfacing, I would like to take over the
> task for persistent events.
> What is the status of the series, is it close to acceptance?
>
> AFAICS the patch RFC 12/12 was under discussion, mainly about the
> naming of the ioctls (latest e-mail is in favor of CLAIM/UNCLAIM).
>
> Any thoughts?
>
> Let me rebase the code against the latest mainline and re-start the discussion.

That's nice, cool. However, before this thing goes upstream, Ingo wanted
to have also a user for the events, i.e. persistent events integrated
in perf tool. For that, perf tool functionality has to be made generic
enough and thus usable for other tools.

I have started doing that but other stuff preempted me, as it happens :(.
Here's how a splitup would look like, from an older email from Ingo. In
any case, this would need further discussion but I think it is a good
start.

I'm willing to help out as time permits and I'd venture a guess that
Robert would do that too, so please CC us your submissions.

Thanks!

--
From mingo.kernel.org@gmail.com Tue Nov 26 19:17:58 2013
Date: Tue, 26 Nov 2013 19:17:45 +0100
From: Ingo Molnar <mingo@kernel.org>
To: Borislav Petkov <bp@alien8.de>
Cc: Arnaldo Carvalho de Melo <acme@infradead.org>, LKML
<linux-kernel@vger.kernel.org>, Borislav Petkov <bp@suse.de>, Jiri Olsa
<jolsa@redhat.com>, Peter Zijlstra <peterz@infradead.org>, Robert Richter
<rric@kernel.org>
Subject: Re: [PATCH] perf: Move fs.* to generic lib/lk/
Message-ID: <20131126181745.GD9958@gmail.com>
User-Agent: Mutt/1.5.21 (2010-09-15)
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Content-Type: text/plain; charset=utf-8
Status: RO
X-Status: A


* Borislav Petkov <bp@alien8.de> wrote:

> On Fri, Nov 22, 2013 at 04:39:11PM +0100, Ingo Molnar wrote:
>
> > I see no problem with that - it's basically like util/*.c is, just
> > between tools.
>
> But why? Why it is a good thing to have to pay attention to linking
> to 10 minilibs when you're using 10 utilities for your tool instead
> of a small number of topic libraries, 2-3 tops?

It's a single line added to the Makefile, the moment a .h is used for
the first time. That's not any appreciable overhead.

This would also allow us to farm out most of tools/perf/util/ into
tools/lib/, without any noticeable changes in build performance or
build dependencies. Down the line it would (hopefully) result in code
improvements to these infrastructure bits, sourced from different
tools.

> What's wrong with the split:
>
> * generic stuff
> * trace events
> * perf events
>
> ?

Well, the natural evolution of interfaces ended up with such a split
up:

comet:~/tip/tools/perf> ls util/*.h
util/annotate.h util/hist.h util/strbuf.h
util/build-id.h util/intlist.h util/strfilter.h
util/cache.h util/levenshtein.h util/strlist.h
util/callchain.h util/machine.h util/svghelper.h
util/cgroup.h util/map.h util/symbol.h
util/color.h util/parse-events.h util/target.h
util/comm.h util/parse-options.h util/thread.h
util/cpumap.h util/perf_regs.h util/thread_map.h
util/data.h util/pmu.h util/tool.h
util/debug.h util/probe-event.h util/top.h
util/dso.h util/probe-finder.h util/trace-event.h
util/dwarf-aux.h util/pstack.h util/types.h
util/event.h util/quote.h util/unwind.h
util/evlist.h util/rblist.h util/util.h
util/evsel.h util/run-command.h util/values.h
util/exec_cmd.h util/session.h util/vdso.h
util/fs.h util/sigchain.h util/xyarray.h
util/header.h util/sort.h
util/help.h util/stat.h

If we want additional structure to it then it should be done via the
namespace, not by forcing them into bigger .a's. So this kind of extra
structure makes sense:

api/types/rbtree.h
api/types/strbuf.h
api/formats/dwarf/unwind.h
api/kernel/pmu.h
api/kernel/cgroup.h
api/kernel/debugfs.h

But stuffing them into types.a, formats.a, kernel.a, not so much.

> With "generic stuff" being something like glibc. There's hardly a
> tool that needs/links to *all* of glibs's functionality yet glibs
> doesn't get split. Do you see what I mean?

glibc being such a catch-all library is:

- partly a historic artifact caused by other constraints that don't
affect our tooling landscape here

- partly a political artifact caused by thinking that does not affect
our tooling landscape

- partly a technological mistake.

There's no need for us to repeat that, at least at this stage.

> > What dependencies do you mean? The only constraint is to not make
> > it circular - but that's easy to do if they are nicely separated
> > per concept. I don't think rbtree.h ever wants to include cmdline
> > processing or debugfs processing.
>
> But if you have a single .a library, you don't care about which
> minilibrary to link to what. You basically do take libkapi.a and
> you're good to go - no need to hunt every dependency.

You still need to figure out the .h file - at that point, when you are
using it for the first time in your tool project, you add the .c file
to the Makefile - it's not hard and there are real advantages.

> With the split above, for example, libkapi.a links to glibc only.
> libtraceevent.a and libperfevent.a both link to libkapi.a and glibc.
> It is all nice and clean.

It does not look that nice and clean once I consider all the nice
helpers that exist in util/*.[ch] - and which we'd like to share as
well.

Thanks,

Ingo


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