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Date:	Wed, 17 Nov 2010 13:21:43 +0100
From:	Peter Zijlstra <>
To:	Jeremy Fitzhardinge <>
Cc:	Linux Kernel Mailing List <>,
	Nick Piggin <>,
	Mathieu Desnoyers <>,
	Américo Wang <>,
	Eric Dumazet <>,
	Jan Beulich <>, Avi Kivity <>,
	Xen-devel <>,
	"H. Peter Anvin" <>,
	Linux Virtualization <>,
	Srivatsa Vaddagiri <>,
	Jeremy Fitzhardinge <>
Subject: Re: [PATCH 13/14] x86/ticketlock: add slowpath logic

On Tue, 2010-11-16 at 13:08 -0800, Jeremy Fitzhardinge wrote:
> Maintain a flag in both LSBs of the ticket lock which indicates whether
> anyone is in the lock slowpath and may need kicking when the current
> holder unlocks.  The flags are set when the first locker enters
> the slowpath, and cleared when unlocking to an empty queue.

So here you say you set both LSBs in order to keep head == tail working,
but the code seems to suggest you only use the tail LSB.

I think I see why using only one LSB is sufficient, but some consistency
would be nice :-)
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