From mboxrd@z Thu Jan 1 00:00:00 1970 From: Arnd Bergmann Subject: Re: [PATCH 01/23] all: syscall wrappers: add documentation Date: Wed, 25 May 2016 23:01:06 +0200 Message-ID: <6407614.fdv5XFSBue@wuerfel> References: <20160525200327.GA22395@yury-N73SV> <6293194.tGy03QJ9ME@wuerfel> <20160525.135039.244098606649448826.davem@davemloft.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7Bit Return-path: Received: from mout.kundenserver.de ([212.227.126.134]:59486 "EHLO mout.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750867AbcEYVCU (ORCPT ); Wed, 25 May 2016 17:02:20 -0400 In-Reply-To: <20160525.135039.244098606649448826.davem@davemloft.net> Sender: linux-arch-owner@vger.kernel.org List-ID: To: David Miller Cc: ynorov@caviumnetworks.com, catalin.marinas@arm.com, linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, linux-arch@vger.kernel.org, linux-s390@vger.kernel.org, libc-alpha@sourceware.org, schwidefsky@de.ibm.com, heiko.carstens@de.ibm.com, pinskia@gmail.com, broonie@kernel.org, joseph@codesourcery.com, christoph.muellner@theobroma-systems.com, bamvor.zhangjian@huawei.com, szabolcs.nagy@arm.com, klimov.linux@gmail.com, Nathan_Lynch@mentor.com, agraf@suse.de, Prasun.Kapoor@caviumnetworks.com, kilobyte@angband.pl, geert@linux-m68k.org, philipp.tomsich@theobroma-systems.com On Wednesday, May 25, 2016 1:50:39 PM CEST David Miller wrote: > From: Arnd Bergmann > Date: Wed, 25 May 2016 22:47:33 +0200 > > > If we use the normal calling conventions, we could remove these overrides > > along with the respective special-case handling in glibc. None of them > > look particularly performance-sensitive, but I could be wrong there. > > You could set the lowest bit in the system call entry pointer to indicate > the upper-half clears should be elided. Right, but that would introduce an extra conditional branch in the syscall hotpath, and likely eliminate the gains from passing the loff_t arguments in a single register instead of a pair. Arnd