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[Xen-devel] Re: [PATCH 2/3] kvm hypervisor : Add hypercalls to support p

To: vatsa@xxxxxxxxxxxxxxxxxx
Subject: [Xen-devel] Re: [PATCH 2/3] kvm hypervisor : Add hypercalls to support pv-ticketlock
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Thu, 20 Jan 2011 14:41:46 +0100
Cc: Mathieu, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Desnoyers <mathieu.desnoyers@xxxxxxxxxx>, Nick Piggin <npiggin@xxxxxxxxx>, Jeremy, Linux, Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Beulich <JBeulich@xxxxxxxxxx>, Linux Kernel Mailing List <linux-kernel@xxxxxxxxxxxxxxx>, Jan, Fitzhardinge <jeremy.fitzhardinge@xxxxxxxxxx>, suzuki@xxxxxxxxxx, Avi Kivity <avi@xxxxxxxxxx>, kvm@xxxxxxxxxxxxxxx, "H. Peter Anvin" <hpa@xxxxxxxxx>, Américo Wang <xiyou.wangcong@xxxxxxxxx>, Eric Dumazet <dada1@xxxxxxxxxxxxx>, Virtualization <virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx>
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On Thu, 2011-01-20 at 17:29 +0530, Srivatsa Vaddagiri wrote:
> If we had a yield-to [1] sort of interface _and_ information on which vcpu
> owns a lock, then lock-spinners can yield-to the owning vcpu, 

and then I'd nak it for being stupid ;-)

really, yield*() is retarded, never even consider using it. If you've
got the actual owner you can do full blown PI, which is tons better than
a 'do-something-random' call.

The only reason the whole non-virt pause loop filtering muck uses it is
because it really doesn't know anything, and do-something is pretty much
all it can do. Its a broken interface.

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