Re: [PATCH v2 4/8] powerpc/vdso32: inline __get_datapage()

[Christophe Leroy]

Le 13/09/2019 Ã 15:31, Santosh Sivaraj a ÃcritÂ:
> Christophe Leroy <christophe.leroy@xxxxxx> writes:
>
> > Hi Santosh,
> >
> > Le 26/08/2019 Ã 07:44, Santosh Sivaraj a ÃcritÂ:
> > > Hi Christophe,
> > >
> > > Christophe Leroy <christophe.leroy@xxxxxx> 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@xxxxxx>
> > > > ---
> > > >    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