From mboxrd@z Thu Jan  1 00:00:00 1970
From: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
Subject: Re: [PATCH 2/3] kvm hypervisor : Add hypercalls to support
 pv-ticketlock
Date: Thu, 20 Jan 2011 20:04:30 +0530
Message-ID: <20110120143430.GA17815@linux.vnet.ibm.com>
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Cc: Jeremy Fitzhardinge <jeremy@goop.org>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Nick Piggin <npiggin@kernel.dk>,
	Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>,
	=?iso-8859-1?Q?Am=E9rico?= Wang <xiyou.wangcong@gmail.com>,
	Eric Dumazet <dada1@cosmosbay.com>,
	Jan Beulich <JBeulich@novell.com>, Avi Kivity <avi@redhat.com>,
	Xen-devel <xen-devel@lists.xensource.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Linux Virtualization <virtualization@lists.linux-foundation.org>,
	Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>,
	kvm@vger.kernel.org, suzuki@in.ibm.com
To: Peter Zijlstra <peterz@infradead.org>
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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