Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933670AbWKTUNw (ORCPT ); Mon, 20 Nov 2006 15:13:52 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S934114AbWKTUNw (ORCPT ); Mon, 20 Nov 2006 15:13:52 -0500 Received: from brick.kernel.dk ([62.242.22.158]:2380 "EHLO kernel.dk") by vger.kernel.org with ESMTP id S933670AbWKTUNv (ORCPT ); Mon, 20 Nov 2006 15:13:51 -0500 Date: Mon, 20 Nov 2006 21:13:35 +0100 From: Jens Axboe To: Alan Stern Cc: "Paul E. McKenney" , Oleg Nesterov , Kernel development list Subject: Re: [patch] cpufreq: mark cpufreq_tsc() as core_initcall_sync Message-ID: <20061120201334.GE8055@kernel.dk> References: <20061120175848.GD8055@kernel.dk> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1781 Lines: 41 On Mon, Nov 20 2006, Alan Stern wrote: > On Mon, 20 Nov 2006, Jens Axboe wrote: > > > On Mon, Nov 20 2006, Alan Stern wrote: > > > Paul: > > > > > > Here's my version of your patch from yesterday. It's basically the same, > > > but I cleaned up the code in a few places and fixed a bug (the sign of idx > > > in srcu_read_unlock). Also I changed the init routine back to void, since > > > it's no longer an error if the per-cpu allocation fails. > > > > > > More importantly, I added a static initializer and included the fast-path > > > in synchronize_srcu. It's protected by the new symbol > > > SMP__STORE_MB_LOAD_WORKS, which should be defined in arch-specific headers > > > for those architectures where the store-mb-load pattern is safe. > > > > Must we introduce memory allocations in srcu_read_lock()? It makes it > > much harder and nastier for me to use. I'd much prefer a failing > > init_srcu(), seems like a much better API. > > Paul agrees with you that allocation failures in init_srcu() should be > passed back to the caller, and I certainly don't mind doing so. > > However we can't remove the memory allocation in srcu_read_lock(). That > was the point which started this whole thread: the per-cpu allocation > cannot be done statically, and some users of a static SRCU structure can't > easily call init_srcu() early enough. > > Once the allocation succeeds, the overhead in srcu_read_lock() is minimal. It's not about the overhead, it's about a potentially problematic allocation. -- Jens Axboe - 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/