From owner-freebsd-arch@FreeBSD.ORG  Mon Mar 10 13:45:37 2008
Return-Path: <owner-freebsd-arch@FreeBSD.ORG>
Delivered-To: freebsd-arch@FreeBSD.org
Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34])
	by hub.freebsd.org (Postfix) with ESMTP id 1F6BC1065677
	for <freebsd-arch@FreeBSD.org>; Mon, 10 Mar 2008 13:45:37 +0000 (UTC)
	(envelope-from rwatson@FreeBSD.org)
Received: from cyrus.watson.org (cyrus.watson.org [209.31.154.42])
	by mx1.freebsd.org (Postfix) with ESMTP id 0D4D18FC16
	for <freebsd-arch@FreeBSD.org>; Mon, 10 Mar 2008 13:45:37 +0000 (UTC)
	(envelope-from rwatson@FreeBSD.org)
Received: from fledge.watson.org (fledge.watson.org [209.31.154.41])
	by cyrus.watson.org (Postfix) with ESMTP id 983FA46B0D;
	Mon, 10 Mar 2008 08:45:36 -0500 (EST)
Date: Mon, 10 Mar 2008 14:45:36 +0100 (BST)
From: Robert Watson <rwatson@FreeBSD.org>
X-X-Sender: robert@fledge.watson.org
To: Skalla Raabjorn <skalla.raabjorn@gmx.de>
In-Reply-To: <20080310140753.24630bda@sol.hackerzberg.local>
Message-ID: <20080310143919.V50827@fledge.watson.org>
References: <20080310140753.24630bda@sol.hackerzberg.local>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed
Cc: freebsd-arch@FreeBSD.org
Subject: Re: If GIANT is locked can the MPSAFE parts run in parallel?
X-BeenThere: freebsd-arch@freebsd.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Discussion related to FreeBSD architecture <freebsd-arch.freebsd.org>
List-Unsubscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-arch>,
	<mailto:freebsd-arch-request@freebsd.org?subject=unsubscribe>
List-Archive: <http://lists.freebsd.org/pipermail/freebsd-arch>
List-Post: <mailto:freebsd-arch@freebsd.org>
List-Help: <mailto:freebsd-arch-request@freebsd.org?subject=help>
List-Subscribe: <http://lists.freebsd.org/mailman/listinfo/freebsd-arch>,
	<mailto:freebsd-arch-request@freebsd.org?subject=subscribe>
X-List-Received-Date: Mon, 10 Mar 2008 13:45:37 -0000


On Mon, 10 Mar 2008, Skalla Raabjorn wrote:

> if GIANT is locked can the MPSAFE parts run in parallel? Like networking for 
> example, as they have their own locks.

Dear Skalla,

Yes.  Giant is [almost] a mutex like any other mutex, so as long as the MPSAFE 
subsystem isn't being invoked by something holding Giant, it generally won't 
run with it.  Even if the network stack is sometimes executed with Giant held 
(for example, when receiving a packet from SLIP), that doesn't prevent the 
network stack from executing in parallel on other CPUs, it just serializes 
with respect to other Giant holders executing.

Robert N M Watson
Computer Laboratory
University of Cambridge