linux-kernel - Re: [PATCH v3 4/8] powerpc/vdso32: inline __get

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Message-ID: <87sgm8zhw0.fsf@mpe.ellerman.id.au>
Date:   Thu, 28 Nov 2019 16:31:27 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Christophe Leroy <christophe.leroy@....fr>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>
Cc:     linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH v3 4/8] powerpc/vdso32: inline __get_datapage()

Christophe Leroy <christophe.leroy@....fr> writes:
> Le 22/11/2019 à 07:38, Michael Ellerman a écrit :
>> Michael Ellerman <mpe@...erman.id.au> writes:
>>> Christophe Leroy <christophe.leroy@....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@....fr>
>>>
>>> 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.

cheers