From owner-cvs-src@FreeBSD.ORG  Thu Jul 29 20:26:14 2004
Return-Path: <owner-cvs-src@FreeBSD.ORG>
Delivered-To: cvs-src@freebsd.org
Received: from mx1.FreeBSD.org (mx1.freebsd.org [216.136.204.125])
	by hub.freebsd.org (Postfix) with ESMTP
	id 9ECEB16A4CF; Thu, 29 Jul 2004 20:26:14 +0000 (GMT)
Received: from pooker.samsco.org (pooker.samsco.org [168.103.85.57])
	by mx1.FreeBSD.org (Postfix) with ESMTP
	id 4506643D58; Thu, 29 Jul 2004 20:26:14 +0000 (GMT)
	(envelope-from scottl@freebsd.org)
Received: from pooker.samsco.org (scottl@localhost [127.0.0.1])
	by pooker.samsco.org (8.12.11/8.12.10) with ESMTP id i6TKXCgA020305;
	Thu, 29 Jul 2004 14:33:12 -0600 (MDT)
	(envelope-from scottl@freebsd.org)
Received: from localhost (scottl@localhost)i6TKXBoc020302;
	Thu, 29 Jul 2004 14:33:11 -0600 (MDT)
	(envelope-from scottl@freebsd.org)
X-Authentication-Warning: pooker.samsco.org: scottl owned process doing -bs
Date: Thu, 29 Jul 2004 14:33:11 -0600 (MDT)
From: Scott Long <scottl@freebsd.org>
Sender: scottl@pooker.samsco.org
To: Alan Cox <alc@cs.rice.edu>
In-Reply-To: <20040729200841.GF18577@cs.rice.edu>
Message-ID: <20040729143241.I32601@pooker.samsco.org>
References: <20040729131040.F32601@pooker.samsco.org>
 <Pine.NEB.3.96L.1040729154004.46374J-100000@fledge.watson.org>
 <20040729200841.GF18577@cs.rice.edu>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII
X-Spam-Status: No, hits=0.0 required=3.8 tests=none autolearn=no version=2.63
X-Spam-Checker-Version: SpamAssassin 2.63 (2004-01-11) on pooker.samsco.org
cc: Alan Cox <alc@freebsd.org>
cc: cvs-src@freebsd.org
cc: src-committers@freebsd.org
cc: Robert Watson <rwatson@freebsd.org>
cc: cvs-all@freebsd.org
Subject: Re: cvs commit: src/sys/alpha/alpha pmap.c src/sys/amd64/amd64pmap.c
 src/sys/i386/i386 pmap.c src/sys/vm vm_page.c
X-BeenThere: cvs-src@freebsd.org
X-Mailman-Version: 2.1.1
Precedence: list
List-Id: CVS commit messages for the src tree <cvs-src.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/cvs-src>,
	<mailto:cvs-src-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/cvs-src>
List-Post: <mailto:cvs-src@freebsd.org>
List-Help: <mailto:cvs-src-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/cvs-src>,
	<mailto:cvs-src-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Thu, 29 Jul 2004 20:26:14 -0000

On Thu, 29 Jul 2004, Alan Cox wrote:
> On Thu, Jul 29, 2004 at 03:41:03PM -0400, Robert Watson wrote:
> > On Thu, 29 Jul 2004, Scott Long wrote:
> >
> > > >    - Enable recursion on the page queues lock.  This allows calls to
> > > >      vm_page_alloc(VM_ALLOC_NORMAL) and UMA's obj_alloc() with the page
> > > >      queues lock held.  Such calls are made to allocate page table pages
> > > >      and pv entries.
> > >
> > > My understanding is that recursive mutexes are quite expensive.  Is
> > > recursion a common occurrance now, and is there a good way to
> > > profile/measure these paths?
> >
> > No opinion on the change itself, but just to clarify this wording a little
> > for those reading who don't follow the locking work blow-by-blow: flagging
> > a mutex as recursive itself is not expensive, but the act of recursing the
> > mutex is expensive.
> >
>
> I've benchmarked these changes on alpha, amd64 and i386 under
> buildworld.  The overhead is small.
>
> Also, recursion on the mutex will be rare, occurring under conditions
> of an empty or near-empty free list.

Great!  Thanks for all of your work here =-)

Scott