[PATCH v6 RESEND 0/2] use static key to optimize pgtable_l4_enabled
Jessica Clarke
jrtc27 at jrtc27.com
Wed Jan 11 12:51:54 PST 2023
On 11 Jan 2023, at 19:00, Andrew Jones <ajones at ventanamicro.com> wrote:
> On Thu, Jan 12, 2023 at 01:28:40AM +0800, Jisheng Zhang wrote:
>> On Sun, Dec 11, 2022 at 06:44:04PM +0800, Jisheng Zhang wrote:
>>> On Sat, Oct 08, 2022 at 10:28:35PM +0800, Jisheng Zhang wrote:
>>>> On Thu, Oct 06, 2022 at 04:37:57PM +0800, Jisheng Zhang wrote:
>>>>> On Wed, Oct 05, 2022 at 06:05:28PM -0700, Palmer Dabbelt wrote:
>>>>>> On Sun, 21 Aug 2022 07:09:16 PDT (-0700), jszhang at kernel.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.
>>>>>
>>>>> Hi Palmer,
>>>>>
>>>>> Before V4, there is a bug which can cause kernel panic when SPARSEMEM
>>>>> is enabled, V4 have fixed it by moving the riscv_finalise_pgtable_lx()
>>>>> after sparse_init(). And I just tested the riscv-pgtable_static_key
>>>>> branch in your tree, enabling KASAN and SPARSEMEM, system booted fine.
>>>>> I'm not sure what happened. Could you please send me your kernel
>>>>> config file? I want to fix any issue which can block this series being
>>>>> merged in 6.1-rc1.
>>>>
>>>> Hi Palmer,
>>>>
>>>> I know you are busy ;) Do you have time to send me your test kernel
>>>> config file so that I can reproduce the "early boot hang"?
>>>>
>>>> Thanks
>>>
>>> Hi Palmer,
>>>
>>> I think the early boot hangs maybe the same as the one which has been
>>> fixed by commit 9f2ac64d6ca6 ("riscv: mm: add missing memcpy in
>>> kasan_init"). Will you give this series another try for v6.2-rc1? If
>>> the boot hang can still be reproduced, could you please send me your
>>> .config file?
>>>
>>> Thanks in advance
>> Hi all,
>>
>> Just request to comment what to do with this patch, I think there
>> are two independent points to consult:
>>
>> 1. IIRC, Palmer gave this patch two chances to merge in early versions
>> but he found boot hangs if enable KASAN and SPARSEMEM, while I can't
>> reproduce the boot hang. And I also expect the hang should be fixed by
>> commit 9f2ac64d6ca6 ("riscv: mm: add missing memcpy in kasan_init")
>>
>> 2. Now we know alternative is preferred than static branch for ISA
>> extensions dynamic code patching. So we also need to switch static
>> branch usage here to alternative mechanism, but the problem is
>> SV48 and SV57 are not ISA extensions, so we can't directly make use
>> of the recently introduced riscv_has_extension_likely|unlikely()[1]
>> which is based on alternative mechanism.
>
> We could rename the "has_extension" framework to "has_cpufeature" and
> then lump extensions and features such as sv48 and sv57 together. Or,
> if it's best to keep extensions separate, then duplicate the framework
> to create a "has_non_extension_feature" version where features like
> sv48 and sv57 live.
Sv39, Sv48 and Sv57 are extensions these days (see the draft profiles
spec[1] and [2]).
Jess
[1] https://github.com/riscv/riscv-profiles/blob/main/profiles.adoc#522-rva20s64-mandatory-extensions
[2] https://wiki.riscv.org/display/HOME/Recently+Ratified+Extensions
> Thanks,
> drew
>
>>
>> Any comments are appreciated.
>>
>> Thanks in advance
>>
>> [1] https://lore.kernel.org/linux-riscv/20230111171027.2392-1-jszhang@kernel.org/T/#t
>>
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