Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263625AbUAaGBO (ORCPT ); Sat, 31 Jan 2004 01:01:14 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S263796AbUAaGBO (ORCPT ); Sat, 31 Jan 2004 01:01:14 -0500 Received: from ebiederm.dsl.xmission.com ([166.70.28.69]:12618 "EHLO ebiederm.dsl.xmission.com") by vger.kernel.org with ESMTP id S263625AbUAaGBM (ORCPT ); Sat, 31 Jan 2004 01:01:12 -0500 To: Jamie Lokier Cc: Ulrich Drepper , john stultz , lkml Subject: Re: [RFC][PATCH] linux-2.6.2-rc2_vsyscall-gtod_B1.patch References: <1075344395.1592.87.camel@cog.beaverton.ibm.com> <401894DA.7000609@redhat.com> <20040129132623.GB13225@mail.shareable.org> <20040131024100.GA9236@mail.shareable.org> From: ebiederm@xmission.com (Eric W. Biederman) Date: 30 Jan 2004 22:54:19 -0700 In-Reply-To: <20040131024100.GA9236@mail.shareable.org> Message-ID: User-Agent: Gnus/5.0808 (Gnus v5.8.8) Emacs/21.2 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1246 Lines: 24 Jamie Lokier writes: > Eric W. Biederman wrote: > > With the x86-64 optimized vsyscall the syscall number does > > not need to be placed into a register, because you have used > > the proper entry point. For any syscall worth tuning in > > user space I suspect that level of optimization would be > > beneficial. A fast call path that does not waste a register. > > The cost of loading a constant into a register is _much_ lower than > the cost of indirect jumps which we have been discussing. I was thinking more of the register pressure in the load. But in the case of gettimeofday I think it makes to do a kernel implementation that is argument compatible with libc and then linker magic could just short circuit the calls to the vsyscall page and libc would not need to get involved at all, which removes one of the indirect calls. We could probably do that today by just renaming the function gettimeofday. But that is rude and has name space pollution issues. Eric - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/