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spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from bilbo.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 4CF5WS2kqFzDqcK for ; Mon, 19 Oct 2020 16:52:36 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=csgroup.eu (client-ip=93.17.236.30; helo=pegase1.c-s.fr; envelope-from=christophe.leroy@csgroup.eu; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=csgroup.eu Received: from pegase1.c-s.fr (pegase1.c-s.fr [93.17.236.30]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4CF5TZ0Zz8zDqZ3 for ; Mon, 19 Oct 2020 16:50:51 +1100 (AEDT) Received: from localhost (mailhub1-int [192.168.12.234]) by localhost (Postfix) with ESMTP id 4CF5TC3zYTzB09ZK; Mon, 19 Oct 2020 07:50:39 +0200 (CEST) X-Virus-Scanned: Debian amavisd-new at c-s.fr Received: from pegase1.c-s.fr ([192.168.12.234]) by localhost (pegase1.c-s.fr [192.168.12.234]) (amavisd-new, port 10024) with ESMTP id sYt0Xg4oCd0o; Mon, 19 Oct 2020 07:50:39 +0200 (CEST) Received: from messagerie.si.c-s.fr (messagerie.si.c-s.fr [192.168.25.192]) by pegase1.c-s.fr (Postfix) with ESMTP id 4CF5TC2z5GzB09ZJ; Mon, 19 Oct 2020 07:50:39 +0200 (CEST) Received: from localhost (localhost [127.0.0.1]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 4DD4A8B78A; Mon, 19 Oct 2020 07:50:44 +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 68d6s7Q7joVC; Mon, 19 Oct 2020 07:50:44 +0200 (CEST) Received: from [10.25.210.27] (unknown [10.25.210.27]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 0CA6A8B75E; Mon, 19 Oct 2020 07:50:44 +0200 (CEST) Subject: Re: [PATCH] asm-generic: Force inlining of get_order() to work around gcc10 poor decision To: Joel Stanley , Segher Boessenkool References: <96c6172d619c51acc5c1c4884b80785c59af4102.1602949927.git.christophe.leroy@csgroup.eu> From: Christophe Leroy Message-ID: <0bd0afae-f043-2811-944b-c94d90e231d2@csgroup.eu> Date: Mon, 19 Oct 2020 07:50:41 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.12.1 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: linux-arch@vger.kernel.org, Arnd Bergmann , Linux Kernel Mailing List , Masahiro Yamada , Andrew Morton , linuxppc-dev Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Le 19/10/2020 à 06:55, Joel Stanley a écrit : > On Sat, 17 Oct 2020 at 15:55, Christophe Leroy > wrote: >> >> When building mpc885_ads_defconfig with gcc 10.1, >> the function get_order() appears 50 times in vmlinux: >> >> [linux]# ppc-linux-objdump -x vmlinux | grep get_order | wc -l >> 50 >> >> [linux]# size vmlinux >> text data bss dec hex filename >> 3842620 675624 135160 4653404 47015c vmlinux >> >> In the old days, marking a function 'static inline' was forcing >> GCC to inline, but since commit ac7c3e4ff401 ("compiler: enable >> CONFIG_OPTIMIZE_INLINING forcibly") GCC may decide to not inline >> a function. >> >> It looks like GCC 10 is taking poor decisions on this. >> >> get_order() compiles into the following tiny function, >> occupying 20 bytes of text. >> >> 0000007c : >> 7c: 38 63 ff ff addi r3,r3,-1 >> 80: 54 63 a3 3e rlwinm r3,r3,20,12,31 >> 84: 7c 63 00 34 cntlzw r3,r3 >> 88: 20 63 00 20 subfic r3,r3,32 >> 8c: 4e 80 00 20 blr >> >> By forcing get_order() to be __always_inline, the size of text is >> reduced by 1940 bytes, that is almost twice the space occupied by >> 50 times get_order() >> >> [linux-powerpc]# size vmlinux >> text data bss dec hex filename >> 3840680 675588 135176 4651444 46f9b4 vmlinux > > I see similar results with GCC 10.2 building for arm32. There are 143 > instances of get_order with aspeed_g5_defconfig. > > Before: > 9071838 2630138 186468 11888444 b5673c vmlinux > After: > 9069886 2630126 186468 11886480 b55f90 vmlinux > > 1952 bytes smaller with your patch applied. Did you raise this with > anyone from GCC? Yes I did, see https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97445 For the time being, it's at a standstill. Christophe > > Reviewed-by: Joel Stanley > > > >> Signed-off-by: Christophe Leroy >> --- >> include/asm-generic/getorder.h | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >> >> diff --git a/include/asm-generic/getorder.h b/include/asm-generic/getorder.h >> index e9f20b813a69..f2979e3a96b6 100644 >> --- a/include/asm-generic/getorder.h >> +++ b/include/asm-generic/getorder.h >> @@ -26,7 +26,7 @@ >> * >> * The result is undefined if the size is 0. >> */ >> -static inline __attribute_const__ int get_order(unsigned long size) >> +static __always_inline __attribute_const__ int get_order(unsigned long size) >> { >> if (__builtin_constant_p(size)) { >> if (!size) >> -- >> 2.25.0 >>