From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Miller Subject: Re: [PATCH 01/23] all: syscall wrappers: add documentation Date: Thu, 26 May 2016 12:43:44 -0700 (PDT) Message-ID: <20160526.124344.1660236473079504674.davem@davemloft.net> References: <6407614.fdv5XFSBue@wuerfel> <20160525.142821.1719403997976778673.davem@davemloft.net> <20160526142057.GA7456@e104818-lin.cambridge.arm.com> Mime-Version: 1.0 Content-Type: Text/Plain; charset=us-ascii Content-Transfer-Encoding: 7bit Return-path: Received: from shards.monkeyblade.net ([149.20.54.216]:53868 "EHLO shards.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754727AbcEZTnr (ORCPT ); Thu, 26 May 2016 15:43:47 -0400 In-Reply-To: <20160526142057.GA7456@e104818-lin.cambridge.arm.com> Sender: linux-arch-owner@vger.kernel.org List-ID: To: catalin.marinas@arm.com Cc: arnd@arndb.de, ynorov@caviumnetworks.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 From: Catalin Marinas Date: Thu, 26 May 2016 15:20:58 +0100 > We can solve (a) by adding more __SC_WRAP annotations in the generic > unistd.h. ... I really think it's much more robust to clear the tops of the registers by default. Then you won't be auditing constantly and adding more and more wrappers. You can't even quantify the performance gains for me in any precise way. Whatever you gain by avoiding the 64-bit decompostion/reconstitution for those few system calls with 64-bit registers, you are losing by calling the wrappers for more common system calls, more often. "it's more natural to pass 64-bit values in a register" is not a clear justification for this change. This looks way over engineered to me.