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

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Message-ID: <20110120143430.GA17815@linux.vnet.ibm.com>
Date:	Thu, 20 Jan 2011 20:04:30 +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 Thu, Jan 20, 2011 at 02:41:46PM +0100, Peter Zijlstra wrote:
> 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.

Yes definitely that would be much better than yield-to.

> 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.

- vatsa
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