From owner-freebsd-hackers@FreeBSD.ORG Tue Jan 3 19:26:08 2006 Return-Path: X-Original-To: freebsd-hackers@freebsd.org Delivered-To: freebsd-hackers@freebsd.org Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125]) by hub.freebsd.org (Postfix) with ESMTP id 7677D16A41F; Tue, 3 Jan 2006 19:26:08 +0000 (GMT) (envelope-from deischen@freebsd.org) Received: from mail.ntplx.net (mail.ntplx.net [204.213.176.10]) by mx1.FreeBSD.org (Postfix) with ESMTP id 20FB043D58; Tue, 3 Jan 2006 19:26:00 +0000 (GMT) (envelope-from deischen@freebsd.org) Received: from sea.ntplx.net (sea.ntplx.net [204.213.176.11]) by mail.ntplx.net (8.13.5/8.13.5/NETPLEX) with ESMTP id k03JPvhT006786; Tue, 3 Jan 2006 14:25:57 -0500 (EST) Date: Tue, 3 Jan 2006 14:25:57 -0500 (EST) From: Daniel Eischen X-X-Sender: eischen@sea.ntplx.net To: John Baldwin In-Reply-To: <200601031252.42657.jhb@freebsd.org> Message-ID: MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII X-Virus-Scanned: by AMaViS and Clam AntiVirus (mail.ntplx.net) Cc: freebsd-hackers@freebsd.org, prime Subject: Re: An idea of remove MUTEX_WAKE_ALL X-BeenThere: freebsd-hackers@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list Reply-To: Daniel Eischen List-Id: Technical Discussions relating to FreeBSD List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 03 Jan 2006 19:26:08 -0000 On Tue, 3 Jan 2006, John Baldwin wrote: > On Sunday 01 January 2006 02:21 am, prime wrote: > > Hi hackers, > > I have an idea about remove the kernel option MUTEX_WAKE_ALL. > > When we unlock the mutex(in _mtx_unlock_sleep),we can directly > > give the lock to the first thread waiting on the turnstile.And a > > thread gets the mutex after he returned from turnstile_wait so he > > can simply jump out the _obtain_lock loop in _mtx_lock_sleep. > > This makes a mutex always be owned by a thread when there are threads > > waiting on the turnstile,so priority inheritance can work now. > > This idea need only a few changes in kern/kern_mutex.c .But when > > NO_ADAPTIVE_MUTEXS not set,it makes threads that spinning on other CPU > > to get the mutex have to spin for a long time,and this makes the short > > term mutex more expensive(maybe should use spin mutex instead). > > > > What do think about the idea? Thanks. > > Sun actually found that the performance was better when you did MUTEX_WAKE_ALL > because once you woke up N threads, if they don't all resume at once then > they will acquire the lock in sequence and the lock acquires and releaes will > all be simple ones rather than all being the complicated contested case. > There are more details in _Solaris Internals_. Yes, but doesn't this partly rely on having the threads spin(*) for a bit if the current lock owner is running on another CPU? Do we currently do that? (*) No, I am not referring to spin mutexes. -- DE