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Fri, 13 Sep 2019 15:50:07 +0200 (CEST) X-Virus-Scanned: amavisd-new at c-s.fr Received: from messagerie.si.c-s.fr ([127.0.0.1]) by localhost (messagerie.si.c-s.fr [127.0.0.1]) (amavisd-new, port 10023) with ESMTP id GFEzWtWycXeb; Fri, 13 Sep 2019 15:50:07 +0200 (CEST) Received: from [172.25.230.101] (po15451.idsi0.si.c-s.fr [172.25.230.101]) by messagerie.si.c-s.fr (Postfix) with ESMTP id B8C8E8BA91; Fri, 13 Sep 2019 15:50:07 +0200 (CEST) Subject: Re: [PATCH v2 4/8] powerpc/vdso32: inline __get_datapage() To: Santosh Sivaraj , Benjamin Herrenschmidt , Paul Mackerras , Michael Ellerman References: <194fb7bc973ef2ce43016c97dd32f2b2dcbae4e7.1566491310.git.christophe.leroy@c-s.fr> <87h864iiq9.fsf@santosiv.in.ibm.com> <87blvonwzz.fsf@santosiv.in.ibm.com> From: Christophe Leroy Message-ID: <559296a2-37f6-dc83-7f60-07567637a9a8@c-s.fr> Date: Fri, 13 Sep 2019 15:50:07 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <87blvonwzz.fsf@santosiv.in.ibm.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: fr Content-Transfer-Encoding: 8bit X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Le 13/09/2019 à 15:31, Santosh Sivaraj a écrit : > Christophe Leroy writes: > >> Hi Santosh, >> >> Le 26/08/2019 à 07:44, Santosh Sivaraj a écrit : >>> Hi Christophe, >>> >>> Christophe Leroy 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 >>>> --- >>>> 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