Date: Tue, 03 Aug 2004 18:07:21 -0400 From: Stephan Uphoff <ups@tree.com> To: John Baldwin <jhb@FreeBSD.org> Cc: Stephan Uphoff <ups@tree.com> Subject: Re: cvs commit: src/sys/vm vm_map.c vm_map.h Message-ID: <200408032207.i73M7LfY049171@palm.tree.com> In-Reply-To: Message from John Baldwin <jhb@FreeBSD.org> of "Tue, 03 Aug 2004 12:56:15 EDT." <200408031256.15886.jhb@FreeBSD.org>
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John Baldwin wrote: > On Monday 02 August 2004 10:58 pm, Stephan Uphoff wrote: > > John Baldwin wrote: > > > On Friday 30 July 2004 12:06 pm, Brian Fundakowski Feldman wrote: > > > > On Fri, Jul 30, 2004 at 09:10:28AM +0000, Maxime Henrion wrote: > > > > > mux 2004-07-30 09:10:28 UTC > > > > > > > > > > FreeBSD src repository > > > > > > > > > > Modified files: > > > > > sys/vm vm_map.c vm_map.h > > > > > Log: > > > > > Get rid of another lockmgr(9) consumer by using sx locks for the > > > > > user maps. We always acquire the sx lock exclusively here, but we > > > > > can't use a mutex because we want to be able to sleep while holding > > > > > the lock. This is completely equivalent to what we were doing with > > > > > the lockmgr(9) locks before. > > > > > > > > Not that I don't think it's worth doing in general, but is there a > > > > comparison anyone has done between speeds of sx and lockmgr? > > > > > > Speed aside, when allproc_lock and proctree_lock were lockmgr locks > > > (before sx was implemented), my SMP machines routinely locked up and when > > > I looked at things in the debugger it seemed that no one held > > > allproc_lock but several processes were blocked on it. Quite frankly, I > > > don't trust lockmgr()'s implementation. > > > > Since the vfs layer forces me to use the lockmgr you scared me into > > taking a look. > > And yes there is a bug in the current implementation. (kern/69934). > > Good catch! Unfortunately, the problems I was seeing above involved locks > that didn't use upgrade or downgrade. :( Mhhh .. I found another bug (kern/69964). Getting closer? ;-) > I've pondered taking an axe to all > of lockmgr and just rewriting it from scratch to use mutexes and cv's like > sx. I hope to take the axe on the current vfs layer. (Eliminating the need for lockmgr) However it might take a while until I can show/share results. Stephan
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