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Date:   Tue, 26 Jul 2022 18:17:10 -0300
From:   Arnaldo Carvalho de Melo <acme@kernel.org>
To:     Ian Rogers <irogers@google.com>
Cc:     Alan Bartlett <ajb@elrepo.org>, Leo Yan <leo.yan@linaro.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@redhat.com>,
        linux-perf-users@vger.kernel.org, ElRepo <contact@elrepo.org>,
        Akemi Yagi <toracat@elrepo.org>, Jiri Olsa <jolsa@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Alexander Shishkin <alexander.shishkin@linux.intel.com>,
        Namhyung Kim <namhyung@kernel.org>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] perf scripts python: Let script to be python2 compliant
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Em Tue, Jul 26, 2022 at 01:43:31PM -0700, Ian Rogers escreveu:
> On Tue, Jul 26, 2022 at 12:43 PM Arnaldo Carvalho de Melo
> <acme@kernel.org> wrote:
> >
> > Em Tue, Jul 26, 2022 at 10:52:31AM -0700, Ian Rogers escreveu:
> > > On Tue, Jul 26, 2022 at 9:57 AM Alan Bartlett <ajb@elrepo.org> wrote:
> > > >
> > > > On Mon, 25 Jul 2022 at 16:51, Arnaldo Carvalho de Melo <acme@kernel.org> wrote:
> > > > >
> > > > > Em Mon, Jul 25, 2022 at 06:42:20PM +0800, Leo Yan escreveu:
> > > > > > The mainline kernel can be used for relative old distros, e.g. RHEL 7.
> > > > > > The distro doesn't upgrade from python2 to python3, this causes the
> > > > > > building error that the python script is not python2 compliant.
> > > > > >
> > > > > > To fix the building failure, this patch changes from the python f-string
> > > > > > format to traditional string format.
> > > > >
> > > > > Thanks, applied.
> > > > >
> > > > > - Arnaldo
> > > >
> > > > Leo / Arnaldo,
> > > >
> > > > Applying the patch on top of -5.19-rc8 fixes the problem that we (the
> > > > ELRepo Project) experienced when attempting to build on RHEL7.
> > > >
> > > > So --
> > > >
> > > > Tested-by: Alan Bartlett <ajb@elrepo.org>
> > > >
> > > > Hopefully you will get it to Linus in time for -5.19 GA.
> >
> > > So I'm somewhat concerned about perf supporting unsupported
> > > distributions and this holding the code base back. RHEL7 was launched
> > > 8 years ago (June 10, 2014) and full support ended 3 years ago (August
> > > 6, 2019) [1]. Currently RHEL7 is in "Maintenance Support or
> > > Maintenance Support 2" phase which is defined to mean [2]:
> > >
> > > ```
> > > During the Maintenance Support Phase for Red Hat Enterprise Linux
> > > Version 8 & 9, and Maintenance Support 2 Phase for Red Hat Enterprise
> > > Linux version 7, Red Hat defined Critical and Important impact
> > > Security Advisories (RHSAs) and selected (at Red Hat discretion)
> > > Urgent Priority Bug Fix Advisories (RHBAs) may be released as they
> > > become available. Other errata advisories may be delivered as
> > > appropriate.
> > >
> > > New functionality and new hardware enablement are not planned for
> > > availability in the Maintenance Support (RHEL 8 & 9) Phase and
> > > Maintenance Support 2 (RHEL 7) Phase.
> > > ```
> > >
> > > >From this definition, why would RHEL7 pick up a new perf tool? I don't
> > > think they would and as such we don't need to worry about supporting
> > > it. RHEL8 defaults to python 3 and full support ends for it next year.
> > > Let's set the bar at RHEL8 and not worry about RHEL7 breakages like
> > > this in future. I think the bar for caring should be "will the distro
> > > pick up our code", if we don't do this then we're signing up to not
> > > allowing tools to update for 10 years! If someone is building a kernel
> > > and perf tool on RHEL7 then they should be signing up to also deal
> > > with tool chain issues, which in this case can mean installing
> > > python3.
> >
> > In this specific supporting things that people report using, like was
> > done in this case, isn't such a big problem.
> 
> So there are linters will fire for this code and say it is not
> pythonic. It is only a linter warning vs asking to support an 8 year
> old out of support distribution. There are other cases, such as
> improving the C code structure, where we've failed to land changes
> because of build errors on old distributions. This could indicate perf
> code is wrong or the distribution is wrong. I'm saying that if we
> believe in the perf code being correct and the distribution is out of
> support, then we should keep the perf code as-is and the issue is one
> for user of the out-of-support distribution.
> 
> > Someone reported a problem in a system they used, the author of the code
> > in question posted a patch allowing perf to be used in such old systems,
> > doesn't get in the way of newer systems, small patch, merged, life goes
> > on.
> 
> Right, but we're setting a precedent for supporting out of support
> distributions. If we can say "life goes on" can we land this *current*
> Debian fix?
> https://lore.kernel.org/lkml/20220629034007.332804-1-irogers@google.com/

I'll revisit the discussion with PeterZ...

- Arnaldo
 
> > Sometimes some organizations are stuck with some distro till they can go
> > thru re-certifications, bidding for new hardware, whatever, and then
> > they want to continue using the latest perf on those systems because
> > they want to benefit from new features we're working on that work on
> > such systems. If the cost is small, like in this case, I see no problems
> > to have perf working on such older systems.
> 
> So there's no problem with perf working on old systems. The issue is
> supporting 10 year old unsupported build infrastructure. The fact that
> the build infrastructure is unsupported means we need to carry all the
> fixes in the tools tree and that can mean doing some questionably sane
> things, like supporting python 2 (end of life for 2.5 years) on RHEL7
> (end of full support 3 years ago). RHEL8 still has a year of support,
> so great test that. RHEL7 then fix your tools and perf will work for
> you - where fix means "rpm -i python3", hardly a huge chore.
> 
> Thanks,
> Ian

-- 

- Arnaldo