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Sun, 5 Apr 2020 20:53:37 +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 QxPOLoXO54EU; Sun, 5 Apr 2020 20:53:37 +0200 (CEST) Received: from [192.168.4.90] (unknown [192.168.4.90]) by messagerie.si.c-s.fr (Postfix) with ESMTP id 200BC8B774; Sun, 5 Apr 2020 20:53:36 +0200 (CEST) Subject: Re: [RFC WIP PATCH] powerpc/32: system call implement entry/exit logic in C To: Nicholas Piggin , Benjamin Herrenschmidt , Michael Ellerman , msuchanek@suse.de, Paul Mackerras References: <059c1abd-6be2-25ea-83e0-dcd411b7951b@c-s.fr> <1585898897.1jwur86s6a.astroid@bobo.none> From: Christophe Leroy Message-ID: Date: Sun, 5 Apr 2020 20:53:00 +0200 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.6.0 MIME-Version: 1.0 In-Reply-To: <1585898897.1jwur86s6a.astroid@bobo.none> 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 03/04/2020 à 09:33, Nicholas Piggin a écrit : > Christophe Leroy's on April 1, 2020 9:48 pm: >> >> >> Le 31/03/2020 à 17:22, Christophe Leroy a écrit : >>> That's first try to port PPC64 syscall entry/exit logic in C to PPC32. >>> I've do the minimum to get it work. I have not reworked calls >>> to sys_fork() and friends for instance. >>> >>> For the time being, it seems to work more or less but: >>> - ping reports EINVAL on recvfrom >>> - strace shows NULL instead of strings in call like open() for instance. >> >> For the two above problems, that's because system_call_exception() >> doesn't set orig_gpr3 whereas DoSycall() does in entry_32.S . Is that >> only done on PPC32 ? >> >> With the following line at the begining of system_call_exception(), it >> works perfectly: >> >> regs->orig_gpr3 = r3; > > Oh great, nice work. We should be able to make some simple helpers or > move some things a bit to reduce the amount of ifdefs in the C code. > It doesn't look too bad though. > >> I will now focus on performance to see if we can do something about it. > > What's the performance difference between current asm code just with > always saving NVGPRS vs C? Done new measurement and sent a series. lower values now because the time accounting was done twice as it was still in the ASM part. Before the series, 311 cycles for a null_syscall If adding SAVE_NVGPRS to the entry macro, 335 cycles First patch: 353 cycles ie +13,5% After a few changes, including conditional saving of non volatile registers, I get 325 cycles that is only +4,5%. I thing that's acceptable. Do you see a problem with still saving non volatile registers only when required ? Christophe