From owner-freebsd-arch@FreeBSD.ORG  Wed Mar 19 19:52:02 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 F3755106566B
	for <freebsd-arch@freebsd.org>; Wed, 19 Mar 2008 19:52:01 +0000 (UTC)
	(envelope-from bright@elvis.mu.org)
Received: from elvis.mu.org (elvis.mu.org [192.203.228.196])
	by mx1.freebsd.org (Postfix) with ESMTP id E080F8FC18
	for <freebsd-arch@freebsd.org>; Wed, 19 Mar 2008 19:52:01 +0000 (UTC)
	(envelope-from bright@elvis.mu.org)
Received: by elvis.mu.org (Postfix, from userid 1192)
	id D4CD31A4D7E; Wed, 19 Mar 2008 12:33:22 -0700 (PDT)
Date: Wed, 19 Mar 2008 12:33:22 -0700
From: Alfred Perlstein <alfred@freebsd.org>
To: John Baldwin <jhb@freebsd.org>
Message-ID: <20080319193322.GC67856@elvis.mu.org>
References: <20080307020626.G920@desktop> <20080318235125.G910@desktop>
	<20080319172344.GX67856@elvis.mu.org>
	<200803191526.56761.jhb@freebsd.org>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <200803191526.56761.jhb@freebsd.org>
User-Agent: Mutt/1.4.2.3i
Cc: Daniel Eischen <deischen@freebsd.org>, arch@freebsd.org,
	David Xu <davidxu@freebsd.org>, freebsd-arch@freebsd.org
Subject: Re: Getting rid of the static msleep priority boost
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: Wed, 19 Mar 2008 19:52:02 -0000

* John Baldwin <jhb@freebsd.org> [080319 12:28] wrote:
> On Wednesday 19 March 2008 01:23:44 pm Alfred Perlstein wrote:
> > * Jeff Roberson <jroberson@chesapeake.net> [080319 02:51] wrote:
> > > On Wed, 19 Mar 2008, David Xu wrote:
> > > 
> > > >Daniel Eischen wrote:
> > > >
> > > >>I'm not sure if any of the above remove the priority from the API,
> > > >>but it would be nice to get rid of msleep totally and replace it
> > > >>with an equivalent cv_wait().
> > > >>
> > > >
> > > >And create sleep queue in each cv to get rid of shared sleep queue
> > > >lock ?
> > > 
> > > Some spinlock is required to interlock with the scheduler lock via 
> > > thread_lock().  So I don't think you can get rid of that layer.  You also 
> > > wouldn't want to have the cost of a 'struct sleepqueue' everywhere you 
> > > want a msleep/condvar.
> > > 
> > > I personally don't see any real advantage to using condvar everywhere. 
> > > The only thing you really get is protection against spurious wakeups.
> > 
> > In theory can't you protect the waitq hung off of condvars with
> > the mutex/spinlock used for the condvar instead of a global 
> > (hashed) lock on the global waitq?
> 
> Right now we let people invoke cv_wakeup/signal w/o holding the lock.  I 
> actually took the thread queue out of condvar's back when doing the original 
> sleep queue stuff since it is cheaper space wise.  Instead of each possible 
> condvar having its own set of queue pointers you just have a set of queue 
> pointers for each thread in the system.  Similar to only have a turnstile per 
> thread rather than per lock.

Ok, thank you, need to think about it.

-- 
- Alfred Perlstein