Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756408Ab0DFQV2 (ORCPT ); Tue, 6 Apr 2010 12:21:28 -0400 Received: from mx1.redhat.com ([209.132.183.28]:45508 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751669Ab0DFQVW (ORCPT ); Tue, 6 Apr 2010 12:21:22 -0400 Message-ID: <4BBB5F52.4000403@redhat.com> Date: Tue, 06 Apr 2010 19:20:34 +0300 From: Avi Kivity User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv:1.9.1.9) Gecko/20100330 Fedora/3.0.4-1.fc12 Thunderbird/3.0.4 MIME-Version: 1.0 To: Thomas Gleixner CC: Darren Hart , Alan Cox , Peter Zijlstra , linux-kernel@vger.kernel.org, Ingo Molnar , Eric Dumazet , "Peter W. Morreale" , Rik van Riel , Steven Rostedt , Gregory Haskins , Sven-Thorsten Dietrich , Chris Mason , John Cooper , Chris Wright Subject: Re: [PATCH V2 0/6][RFC] futex: FUTEX_LOCK with optional adaptive spinning References: <1270499039-23728-1-git-send-email-dvhltc@us.ibm.com> <4BBA5305.7010002@redhat.com> <4BBA5C00.4090703@us.ibm.com> <4BBA6279.20802@redhat.com> <4BBA6B6F.7040201@us.ibm.com> <4BBB36FA.4020008@redhat.com> <1270560931.1595.342.camel@laptop> <20100406145128.6324ac9a@lxorguk.ukuu.org.uk> <4BBB531A.4070500@us.ibm.com> <4BBB5C0D.8050602@redhat.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1067 Lines: 29 On 04/06/2010 07:14 PM, Thomas Gleixner wrote: > >> IMO the best solution is to spin in userspace while the lock holder is >> running, fall into the kernel when it is scheduled out. >> > That's just not realistic as user space has no idea whether the lock > holder is running or not and when it's scheduled out without a syscall :) > The kernel could easily expose this information by writing into the thread's TLS area. So: - the kernel maintains a current_cpu field in a thread's tls - lock() atomically writes a pointer to the current thread's current_cpu when acquiring - the kernel writes an invalid value to current_cpu when switching out - a contended lock() retrieves the current_cpu pointer, and spins as long as it is a valid cpu -- error compiling committee.c: too many arguments to function -- 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/