Christophe Leroy [off-list ref] writes:

Le 13/09/2019 à 15:31, Santosh Sivaraj a écrit :

quoted

Christophe Leroy [off-list ref] writes:

quoted

Hi Santosh,

Le 26/08/2019 à 07:44, Santosh Sivaraj a écrit :

quoted

Hi Christophe,

Christophe Leroy [off-list ref] writes:

quoted

__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 <redacted>
---
   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.

I didn't know we build 32 bit vdso for 64 bit big endians. But I don't think
its difficult to do it, might be a bit tricky. We can have two targets from
the same source.

SRC = vdso/*.c
OBJS_32 = $(SRC:.c=vdso32/.o)
OBJS_64 = $(SRC:.c=vdso64/.o)

Something like this would work. Of course, this is out of memory, might have to
do something slightly different for the Makefiles in kernel.

Thanks,
Santosh

Christophe