Re: [PATCH v3 4/8] powerpc/vdso32: inline __get_datapage()

[Christophe Leroy]

On 11/28/2019 05:31 AM, Michael Ellerman wrote:
> Christophe Leroy <christophe.leroy@xxxxxx> writes:
> > Le 22/11/2019 Ã 07:38, Michael Ellerman a ÃcritÂ:
> > > Michael Ellerman <mpe@xxxxxxxxxxxxxx> writes:
> > > > 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>
> > > >
> > > > This doesn't build with gcc 4.6.3:
> > > >
> > > >     /linux/arch/powerpc/kernel/vdso32/gettimeofday.S: Assembler messages:
> > > >     /linux/arch/powerpc/kernel/vdso32/gettimeofday.S:41: Error: unsupported relocation against __kernel_datapage_offset
> > > >     /linux/arch/powerpc/kernel/vdso32/gettimeofday.S:86: Error: unsupported relocation against __kernel_datapage_offset
> > > >     /linux/arch/powerpc/kernel/vdso32/gettimeofday.S:213: Error: unsupported relocation against __kernel_datapage_offset
> > > >     /linux/arch/powerpc/kernel/vdso32/gettimeofday.S:247: Error: unsupported relocation against __kernel_datapage_offset
> > > >     make[4]: *** [arch/powerpc/kernel/vdso32/gettimeofday.o] Error 1
> > >
> > > Actually I guess it's binutils, which is v2.22 in this case.
> > >
> > > Needed this:
> > >
> > > diff --git a/arch/powerpc/include/asm/vdso_datapage.h b/arch/powerpc/include/asm/vdso_datapage.h
> > > index 12785f72f17d..0048db347ddf 100644
> > > --- a/arch/powerpc/include/asm/vdso_datapage.h
> > > +++ b/arch/powerpc/include/asm/vdso_datapage.h
> > > @@ -117,7 +117,7 @@ extern struct vdso_data *vdso_data;
> > >    .macro get_datapage ptr, tmp
> > >    	bcl	20, 31, .+4
> > >    	mflr	\ptr
> > > -	addi	\ptr, \ptr, __kernel_datapage_offset - (.-4)
> > > +	addi	\ptr, \ptr, (__kernel_datapage_offset - (.-4))@l
> > >    	lwz	\tmp, 0(\ptr)
> > >    	add	\ptr, \tmp, \ptr
> > >    .endm
> >
> > Are you still planning to getting this series merged ? Do you need any
> > help / rebase / re-spin ?
>
> Not sure. I'll possibly send a 2nd pull request next week with it
> included.

v3 conflicts with 2038 cleanup series from Arnd merged yesterday by 
Linus (ceb307474506 ("Merge tag 'y2038-cleanups-5.5' of 
git://git.kernel.org:/pub/scm/linux/kernel/git/arnd/playground"))

Not seen your Ack in that series.

I sent out v4 of my series, rebased on top of 2038 cleanup series.

Christophe