linux-kernel - Re: [PATCH 2/3] kvm hypervisor : Add hypercalls to support pv-ticketlock

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Message-ID: <20110119182940.GA7235@linux.vnet.ibm.com>
Date:	Wed, 19 Jan 2011 23:59:41 +0530
From:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Jeremy Fitzhardinge <jeremy@...p.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>,
	kvm@...r.kernel.org, suzuki@...ibm.com
Subject: Re: [PATCH 2/3] kvm hypervisor : Add hypercalls to support
 pv-ticketlock

On Wed, Jan 19, 2011 at 06:21:12PM +0100, Peter Zijlstra wrote:
> I didn't really read the patch, and I totally forgot everything from
> when I looked at the Xen series, but does the Xen/KVM hypercall
> interface for this include the vcpu to await the kick from?

No not yet, for reasons you mention below.

> My guess is not, since the ticket locks used don't know who the owner
> is, which is of course, sad. There are FIFO spinlock implementations
> that can do this though.. although I think they all have a bigger memory
> footprint.
> 
> The reason for wanting this should be clear I guess, it allows PI.

Yeah - that would be good to experiment with.

- vatsa
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