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xen-devel
[Xen-devel] Re: [PATCH 13/14] x86/ticketlock: add slowpath logic
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To: |
Jeremy Fitzhardinge <jeremy@xxxxxxxx> |
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Subject: |
[Xen-devel] Re: [PATCH 13/14] x86/ticketlock: add slowpath logic |
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From: |
Peter Zijlstra <peterz@xxxxxxxxxxxxx> |
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Date: |
Wed, 17 Nov 2010 13:21:43 +0100 |
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Cc: |
Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxx>, Nick Piggin <npiggin@xxxxxxxxx>, Srivatsa Vaddagiri <vatsa@xxxxxxxxxxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>, Eric Dumazet <dada1@xxxxxxxxxxxxx>, Jeremy Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>, Avi Kivity <avi@xxxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Américo Wang <xiyou.wangcong@xxxxxxxxx>, Linux Virtualization <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx> |
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Wed, 17 Nov 2010 04:23:16 -0800 |
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www-data@xxxxxxxxxxxxxxxxxxx |
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<97ed99ae9160bdb6477284b333bd6708fb7a19cb.1289940821.git.jeremy.fitzhardinge@xxxxxxxxxx> |
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<cover.1289940821.git.jeremy.fitzhardinge@xxxxxxxxxx> <97ed99ae9160bdb6477284b333bd6708fb7a19cb.1289940821.git.jeremy.fitzhardinge@xxxxxxxxxx> |
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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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