linux-kernel - Re: [PATCH v8 00/13] KVM: arm64: PMU: Allow userspace to limit the number of PMCs on vCPU

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Message-ID: <86sf6142x0.wl-maz@kernel.org>
Date:   Mon, 23 Oct 2023 19:19:39 +0100
From:   Marc Zyngier <maz@...nel.org>
To:     Raghavendra Rao Ananta <rananta@...gle.com>
Cc:     Oliver Upton <oliver.upton@...ux.dev>,
        Alexandru Elisei <alexandru.elisei@....com>,
        James Morse <james.morse@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Zenghui Yu <yuzenghui@...wei.com>,
        Shaoqin Huang <shahuang@...hat.com>,
        Jing Zhang <jingzhangos@...gle.com>,
        Reiji Watanabe <reijiw@...gle.com>,
        Colton Lewis <coltonlewis@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v8 00/13] KVM: arm64: PMU: Allow userspace to limit the number of PMCs on vCPU

On Mon, 23 Oct 2023 18:58:19 +0100,
Raghavendra Rao Ananta <rananta@...gle.com> wrote:
> 
> On Mon, Oct 23, 2023 at 6:09 AM Marc Zyngier <maz@...nel.org> wrote:
> >
> > On Fri, 20 Oct 2023 22:40:40 +0100,
> > Raghavendra Rao Ananta <rananta@...gle.com> wrote:
> > >
> > > Hello,
> > >
> > > The goal of this series is to allow userspace to limit the number
> > > of PMU event counters on the vCPU.  We need this to support migration
> > > across systems that implement different numbers of counters.
> >
> > [...]
> >
> > I've gone through the initial patches, and stopped before the tests
> > (which I usually can't be bothered to review anyway).
> >
> > The comments I have a relatively minor and could be applied as fixes
> > on top if Oliver can be convinced to do so. Note that patch #4 has an
> > attribution issue.
> >
> > > base-commit: 0a3a1665cbc59ee8d6326aa6c0b4a8d1cd67dda3
> >
> > maz@...ley-girl:~/hot-poop/arm-platforms$ git describe 0a3a1665cbc59ee8d6326aa6c0b4a8d1cd67dda3
> > fatal: 0a3a1665cbc59ee8d6326aa6c0b4a8d1cd67dda3 is neither a commit nor blob
> >
> > Can you please make an effort to base your postings on a known, stable
> > commit? A tagged -rc would be best. but certainly not a random commit.
> >
> I usually do base on a known -rc. But this series needed a couple of
> series from kvmarm/next (mentioned in the original patch), and hence I
> rebased on top of them.

Well, that commit has since disappeared, as git cannot find it (as
demonstrated above). Which is why I insist on a public tag as a base,
as everything else is completely volatile.

> How do you suggest I handle this in the future? Rebase to a known
> -rc on mainline, apply the required series, and then my series on
> top?

No. You base your own series on an -rc (ideally, -rc3). If there is a
conflict with another series, it is our job (Oliver and I) to fix it
(bonus points if you indicate a resolution for the conflict in the
cover letter).

If there is a hard dependency (something that would actively prevent
your series from working at all), you cherry-pick the minimal set of
patches that makes your own series functional as a *prefix*, and post
the whole thing, including the patches you depend on. Oliver and I
will make sure the common prefix is dealt with without duplication.

And for what it is worth, this series directly applies on v6.6-rc3
without a conflict.

	M.

-- 
Without deviation from the norm, progress is not possible.