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Date: Thu, 20 Jan 2011 00:09:14 +0530
From: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
To: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: Peter Zijlstra <peterz@infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Nick Piggin <npiggin@kernel.dk>,
        Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
        =?iso-8859-1?Q?Am=E9rico?= Wang <xiyou.wangcong@gmail.com>,
        Eric Dumazet <dada1@cosmosbay.com>, Jan Beulich <JBeulich@novell.com>,
        Avi Kivity <avi@redhat.com>, Xen-devel <xen-devel@lists.xensource.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        Linux Virtualization <virtualization@lists.linux-foundation.org>,
        Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>,
        suzuki@in.ibm.com
Subject: Re: [PATCH 13/14] x86/ticketlock: add slowpath logic
Message-ID: <20110119183914.GB7235@linux.vnet.ibm.com>
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References: <cover.1289940821.git.jeremy.fitzhardinge@citrix.com>
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On Wed, Jan 19, 2011 at 10:31:06AM -0800, Jeremy Fitzhardinge wrote:
> I think you're probably right; when I last tested this code, it was
> hanging in at about the rate this kind of race would cause.  And in my
> previous analysis of similar schemes (the current pv spinlock code), it
> was always correct to do the "slowpath" test after doing do the unlock.
> 
> *But* I haven't yet had the chance to specifically go through and
> analyse your patch in detail to make sure there's nothing else going on,
> so take this as provisional.
> 
> How much testing have you given it?

I have tested quite extensively with booting a 16-vcpu guest (on a 16-pcpu host)
and running kernel compine (with 32-threads). Without this patch, I had
difficulty booting/shutting-down successfully (it would hang mid-way).

- vatsa