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SubjectRe: [PATCH v2 4/8] powerpc/vdso32: inline __get_datapage()
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Le 13/09/2019 à 15:31, Santosh Sivaraj a écrit :
> Christophe Leroy <christophe.leroy@c-s.fr> writes:
>
>> Hi Santosh,
>>
>> Le 26/08/2019 à 07:44, Santosh Sivaraj a écrit :
>>> Hi Christophe,
>>>
>>> Christophe Leroy <christophe.leroy@c-s.fr> writes:
>>>
>>>> __get_datapage() is only a few instructions to retrieve the
>>>> address of the page where the kernel stores data to the VDSO.
>>>>
>>>> By inlining this function into its users, a bl/blr pair and
>>>> a mflr/mtlr pair is avoided, plus a few reg moves.
>>>>
>>>> The improvement is noticeable (about 55 nsec/call on an 8xx)
>>>>
>>>> vdsotest before the patch:
>>>> gettimeofday: vdso: 731 nsec/call
>>>> clock-gettime-realtime-coarse: vdso: 668 nsec/call
>>>> clock-gettime-monotonic-coarse: vdso: 745 nsec/call
>>>>
>>>> vdsotest after the patch:
>>>> gettimeofday: vdso: 677 nsec/call
>>>> clock-gettime-realtime-coarse: vdso: 613 nsec/call
>>>> clock-gettime-monotonic-coarse: vdso: 690 nsec/call
>>>>
>>>> Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
>>>> ---
>>>> arch/powerpc/kernel/vdso32/cacheflush.S | 10 +++++-----
>>>> arch/powerpc/kernel/vdso32/datapage.S | 29 ++++-------------------------
>>>> arch/powerpc/kernel/vdso32/datapage.h | 11 +++++++++++
>>>> arch/powerpc/kernel/vdso32/gettimeofday.S | 13 ++++++-------
>>>> 4 files changed, 26 insertions(+), 37 deletions(-)
>>>> create mode 100644 arch/powerpc/kernel/vdso32/datapage.h
>>>
>>> The datapage.h file should ideally be moved under include/asm, then we can use
>>> the same for powerpc64 too.
>>
>> I have a more ambitious project indeed.
>>
>> Most of the VDSO code is duplicated between vdso32 and vdso64. I'm
>> aiming at merging everything into a single source code.
>>
>> This means we would have to generate vdso32.so and vdso64.so out of the
>> same source files. Any idea on how to do that ? I'm not too good at
>> creating Makefiles. I guess we would have everything in
>> arch/powerpc/kernel/vdso/ and would have to build the objects twice,
>> once in arch/powerpc/kernel/vdso32/ and once in arch/powerpc/kernel/vdso64/
>
> Should we need to build the objects twice? For 64 bit config it is going to be
> a 64 bit build else a 32 bit build. It should suffice to get the single source
> code compile for both, maybe with macros or (!)CONFIG_PPC64 conditional
> compilation. Am I missing something when you say build twice?
>

IIUC, on PPC64 we build vdso64 for 64bits user apps and vdso32 for
32bits user apps.

In arch/powerpc/kernel/Makefile, you have:

obj-$(CONFIG_VDSO32) += vdso32/
obj-$(CONFIG_PPC64) += vdso64/

And in arch/powerpc/platforms/Kconfig.cputype, you have:

config VDSO32
def_bool y
depends on PPC32 || CPU_BIG_ENDIAN
help
This symbol controls whether we build the 32-bit VDSO. We obviously
want to do that if we're building a 32-bit kernel. If we're building
a 64-bit kernel then we only want a 32-bit VDSO if we're building for
big endian. That is because the only little endian configuration we
support is ppc64le which is 64-bit only.




Christophe

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