linux-kernel - Re: [PATCH 13/14] x86/ticketlock: add slowpath logic

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Message-ID: <20110119183914.GB7235@linux.vnet.ibm.com>
Date:	Thu, 20 Jan 2011 00:09:14 +0530
From:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
To:	Jeremy Fitzhardinge <jeremy@...p.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Nick Piggin <npiggin@...nel.dk>,
	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>,
	Américo Wang <xiyou.wangcong@...il.com>,
	Eric Dumazet <dada1@...mosbay.com>,
	Jan Beulich <JBeulich@...ell.com>, Avi Kivity <avi@...hat.com>,
	Xen-devel <xen-devel@...ts.xensource.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Linux Virtualization <virtualization@...ts.linux-foundation.org>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@...rix.com>,
	suzuki@...ibm.com
Subject: Re: [PATCH 13/14] x86/ticketlock: add slowpath logic

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
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