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Wed, 19 Feb 2020 09:45:46 +0100 (CET) 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 39Yl18DznLEK; Wed, 19 Feb 2020 09:45:45 +0100 (CET) Received: from [172.25.230.102] (unknown [172.25.230.102]) by messagerie.si.c-s.fr (Postfix) with ESMTP id BA9888B756; Wed, 19 Feb 2020 09:45:45 +0100 (CET) Subject: Re: Surprising code generated for vdso_read_begin() To: Arnd Bergmann , Segher Boessenkool References: <20200109200733.GS3191@gate.crashing.org> <77a8bf25-6615-6c0a-56d4-eae7aa8a8f09@c-s.fr> <20200111113328.GX3191@gate.crashing.org> From: Christophe Leroy Message-ID: <305fcee5-2e1b-ea4d-9a2a-a0e8034d40a8@c-s.fr> Date: Wed, 19 Feb 2020 09:45:45 +0100 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.5.0 MIME-Version: 1.0 In-Reply-To: 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: the arch/x86 maintainers , "linux-kernel@vger.kernel.org" , "open list:BROADCOM NVRAM DRIVER" , Paul Mackerras , Andy Lutomirski , Thomas Gleixner , Vincenzo Frascino , linuxppc-dev , Linux ARM Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Le 16/02/2020 à 19:10, Arnd Bergmann a écrit : > On Sat, Jan 11, 2020 at 12:33 PM Segher Boessenkool > wrote: >> >> On Fri, Jan 10, 2020 at 07:45:44AM +0100, Christophe Leroy wrote: >>> Le 09/01/2020 à 21:07, Segher Boessenkool a écrit : >>>> It looks like the compiler did loop peeling. What GCC version is this? >>>> Please try current trunk (to become GCC 10), or at least GCC 9? >>> >>> It is with GCC 5.5 >>> >>> https://mirrors.edge.kernel.org/pub/tools/crosstool/ doesn't have more >>> recent than 8.1 >> >> Arnd, can you update the tools? We are at 8.3 and 9.2 now :-) Or is >> this hard and/or painful to do? > > To follow up on this older thread, I have now uploaded 6.5, 7.5, 8.3 and 9.2 > binaries, as well as a recent 10.0 snapshot. > Thanks Arnd, I have built the VDSO with 9.2, I get less performant result than with 8.2 (same performance as with 5.5). After a quick look, I see: - Irrelevant NOPs to align loops and stuff, allthough -mpcu=860 should avoid that. - A stack frame is set for saving r31 in __c_kernel_clock_gettime. GCC 8.1 don't need that, all VDSO functions are frameless with 8.1 Christophe