From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner+w=401wt.eu-S1752101AbXA2SQO@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1752101AbXA2SQO (ORCPT <rfc822;w@1wt.eu>);
	Mon, 29 Jan 2007 13:16:14 -0500
Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752539AbXA2SQO
	(ORCPT <rfc822;linux-kernel-outgoing>);
	Mon, 29 Jan 2007 13:16:14 -0500
Received: from omx1-ext.sgi.com ([192.48.179.11]:43256 "EHLO omx1.sgi.com"
	rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP
	id S1752101AbXA2SQM (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Mon, 29 Jan 2007 13:16:12 -0500
Date: Mon, 29 Jan 2007 10:15:54 -0800 (PST)
From: Christoph Lameter <clameter@sgi.com>
To: Peter Zijlstra <a.p.zijlstra@chello.nl>
cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org,
       Andrew Morton <akpm@osdl.org>, Nick Piggin <nickpiggin@yahoo.com.au>,
       Ingo Molnar <mingo@elte.hu>, Rik van Riel <riel@redhat.com>
Subject: Re: [PATCH 00/14] Concurrent Page Cache
In-Reply-To: <1170093944.6189.192.camel@twins>
Message-ID: <Pine.LNX.4.64.0701291013530.29254@schroedinger.engr.sgi.com>
References: <20070128131343.628722000@programming.kicks-ass.net> 
 <Pine.LNX.4.64.0701290918260.28330@schroedinger.engr.sgi.com>
 <1170093944.6189.192.camel@twins>
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

On Mon, 29 Jan 2007, Peter Zijlstra wrote:

> Ladder locking would end up:
> 
> lock A0
> lock B1
> unlock A0 -> a new operation can start
> lock C2
> unlock B1
> lock D5
> unlock C2
> ** we do stuff to D5
> unlock D5
> 

Instead of taking one lock we would need to take 4? Wont doing so cause 
significant locking overhead? We probably would want to run some 
benchmarks. Maybe disable the scheme for systems with a small number of 
processors?