linux-kernel - Re: [PATCH v2] KVM: arm64: nvhe: Fix build with profile optimization

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Date:   Mon, 10 Oct 2022 19:15:36 -0700
From:   Denis Nikitin <denik@...omium.org>
To:     Marc Zyngier <maz@...nel.org>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        David Brazdil <dbrazdil@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, Manoj Gupta <manojgupta@...gle.com>
Subject: Re: [PATCH v2] KVM: arm64: nvhe: Fix build with profile optimization

On Sat, Oct 8, 2022 at 7:22 PM Marc Zyngier <maz@...nel.org> wrote:
>
> On Thu, 06 Oct 2022 17:28:17 +0100,
> Denis Nikitin <denik@...omium.org> wrote:
> >
> > Hi Mark,
>
> s/k/c/
>
> >
> > This problem currently blocks the PGO roll on the ChromeOS kernel and
> > we need some kind of a solution.
>
> I'm sorry, but I don't feel constrained by your internal deadlines. I
> have my own...
>
> > Could you please take a look?
>
> I have asked for a reproducer. All I got for an answer is "this is
> hard". Providing a profiling file would help, for example.

Could you please try the following profile on the 5.15 branch?

$ cat <<EOF > prof.txt
kvm_pgtable_walk:100:10
 2: 5
 3: 5
 5: 5
 6: 5
 10: 5
 10: _kvm_pgtable_walk:50
  5: 5
  7: 5
  10: 5
  13.2: 5
  14: 5
  16: 5 __kvm_pgtable_walk:5
  13: kvm_pgd_page_idx:30
   2: __kvm_pgd_page_idx:30
    2: 5
    3: 5
    5: 5
    2: kvm_granule_shift:5
     3: 5
EOF

$ make LLVM=1 ARCH=arm64 KCFLAGS=-fprofile-sample-use=prof.txt -j8 vmlinux

Thanks,
Denis

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