linux-kernel - Re: [PATCH v2 4/8] powerpc/vdso32: inline __get

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Message-ID: <a95c4a58-bc59-3e75-46db-414f6d0f1412@c-s.fr>
Date:   Fri, 13 Sep 2019 12:59:31 +0200
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Santosh Sivaraj <santosh@...six.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 4/8] powerpc/vdso32: inline __get_datapage()

Hi Santosh,

Le 26/08/2019 à 07:44, Santosh Sivaraj a écrit :
> Hi Christophe,
> 
> 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>
>> ---
>>   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/

Christophe