linux-kernel - Re: [PATCH v6 RESEND 0/2] use static key to optimize pgtable_l4

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Date:   Wed, 05 Oct 2022 18:05:28 -0700 (PDT)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     jszhang@...nel.org
CC:     Paul Walmsley <paul.walmsley@...ive.com>, aou@...s.berkeley.edu,
        ryabinin.a.a@...il.com, glider@...gle.com, andreyknvl@...il.com,
        dvyukov@...gle.com, vincenzo.frascino@....com,
        alexandre.ghiti@...onical.com, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com
Subject:     Re: [PATCH v6 RESEND 0/2] use static key to optimize pgtable_l4_enabled

On Sun, 21 Aug 2022 07:09:16 PDT (-0700), jszhang@...nel.org wrote:
> The pgtable_l4|[l5]_enabled check sits at hot code path, performance
> is impacted a lot. Since pgtable_l4|[l5]_enabled isn't changed after
> boot, so static key can be used to solve the performance issue[1].
>
> An unified way static key was introduced in [2], but it only targets
> riscv isa extension. We dunno whether SV48 and SV57 will be considered
> as isa extension, so the unified solution isn't used for
> pgtable_l4[l5]_enabled now.
>
> patch1 fixes a NULL pointer deference if static key is used a bit earlier.
> patch2 uses the static key to optimize pgtable_l4|[l5]_enabled.
>
> [1] http://lists.infradead.org/pipermail/linux-riscv/2021-December/011164.html
> [2] https://lore.kernel.org/linux-riscv/20220517184453.3558-1-jszhang@kernel.org/T/#t
>
> Since v5:
>  - Use DECLARE_STATIC_KEY_FALSE
>
> Since v4:
>  - rebased on v5.19-rcN
>  - collect Reviewed-by tags
>  - Fix kernel panic issue if SPARSEMEM is enabled by moving the
>    riscv_finalise_pgtable_lx() after sparse_init()
>
> Since v3:
>  - fix W=1 call to undeclared function 'static_branch_likely' error
>
> Since v2:
>  - move the W=1 warning fix to a separate patch
>  - move the unified way to use static key to a new patch series.
>
> Since v1:
>  - Add a W=1 warning fix
>  - Fix W=1 error
>  - Based on v5.18-rcN, since SV57 support is added, so convert
>    pgtable_l5_enabled as well.
>
>
> Jisheng Zhang (2):
>   riscv: move sbi_init() earlier before jump_label_init()
>   riscv: turn pgtable_l4|[l5]_enabled to static key for RV64
>
>  arch/riscv/include/asm/pgalloc.h    | 16 ++++----
>  arch/riscv/include/asm/pgtable-32.h |  3 ++
>  arch/riscv/include/asm/pgtable-64.h | 60 ++++++++++++++++++---------
>  arch/riscv/include/asm/pgtable.h    |  5 +--
>  arch/riscv/kernel/cpu.c             |  4 +-
>  arch/riscv/kernel/setup.c           |  2 +-
>  arch/riscv/mm/init.c                | 64 ++++++++++++++++++-----------
>  arch/riscv/mm/kasan_init.c          | 16 ++++----
>  8 files changed, 104 insertions(+), 66 deletions(-)

Sorry for being slow here, but it looks like this still causes some 
early boot hangs.  Specifically kasan+sparsemem is failing.  As you can 
probably see from the latency I'm still a bit buried right now so I'm 
not sure when I'll have a chance to take more of a look.