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From: Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>
To: Jeremy Fitzhardinge <jeremy@goop.org>
Cc: "Peter Zijlstra" <peterz@infradead.org>,
	"Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
	"Nick Piggin" <npiggin@kernel.dk>,
	"Mathieu Desnoyers" <mathieu.desnoyers@polymtl.ca>,
	"Américo 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>,
	suzuki@in.ibm.com
Subject: Re: [PATCH 13/14] x86/ticketlock: add slowpath logic
Date: Mon, 17 Jan 2011 20:52:22 +0530	[thread overview]
Message-ID: <20110117152222.GA19233@linux.vnet.ibm.com> (raw)
In-Reply-To: <97ed99ae9160bdb6477284b333bd6708fb7a19cb.1289940821.git.jeremy.fitzhardinge@citrix.com>

On Tue, Nov 16, 2010 at 01:08:44PM -0800, Jeremy Fitzhardinge wrote:
> From: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
> 
> 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.
> 
> In the specific implementation of lock_spinning(), make sure to set
> the slowpath flags on the lock just before blocking.  We must do
> this before the last-chance pickup test to prevent a deadlock
> with the unlocker:
> 
> Unlocker			Locker
> 				test for lock pickup
> 					-> fail
> test slowpath + unlock
> 	-> false
> 				set slowpath flags
> 				block
> 
> Whereas this works in any ordering:
> 
> Unlocker			Locker
> 				set slowpath flags
> 				test for lock pickup
> 					-> fail
> 				block
> test slowpath + unlock
> 	-> true, kick

I think this is still racy ..

Unlocker				Locker

				
test slowpath
	-> false
		
				set slowpath flag
				test for lock pickup
					-> fail
				block


unlock

unlock needs to happen first before testing slowpath? I have made that change
for my KVM guest and it seems to be working well with that change .. Will
cleanup and post my patches shortly

- vatsa

  parent reply	other threads:[~2011-01-17 15:22 UTC|newest]

Thread overview: 61+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2010-11-16 21:08 [PATCH 00/14] PV ticket locks without expanding spinlock Jeremy Fitzhardinge
2010-11-16 21:08 ` [PATCH 01/14] x86/ticketlock: clean up types and accessors Jeremy Fitzhardinge
2011-01-11 17:21   ` [Xen-devel] " Konrad Rzeszutek Wilk
2010-11-16 21:08 ` [PATCH 02/14] x86/ticketlock: convert spin loop to C Jeremy Fitzhardinge
2010-11-16 21:08 ` [PATCH 03/14] x86/ticketlock: Use C for __ticket_spin_unlock Jeremy Fitzhardinge
2010-11-16 21:08 ` [PATCH 04/14] x86/ticketlock: make large and small ticket versions of spin_lock the same Jeremy Fitzhardinge
2010-11-16 21:08 ` [PATCH 05/14] x86/ticketlock: make __ticket_spin_lock common Jeremy Fitzhardinge
2010-11-16 21:08 ` [PATCH 06/14] x86/ticketlock: make __ticket_spin_trylock common Jeremy Fitzhardinge
2010-11-16 21:08 ` [PATCH 07/14] x86/spinlocks: replace pv spinlocks with pv ticketlocks Jeremy Fitzhardinge
2010-11-16 21:08 ` [PATCH 08/14] x86/ticketlock: collapse a layer of functions Jeremy Fitzhardinge
2010-11-16 21:08 ` [PATCH 09/14] xen/pvticketlock: Xen implementation for PV ticket locks Jeremy Fitzhardinge
2010-11-17  8:11   ` Jan Beulich
2010-11-17  8:52     ` Jeremy Fitzhardinge
2010-11-17  9:57       ` [Xen-devel] " Jeremy Fitzhardinge
2010-11-17 10:34         ` Jan Beulich
2010-11-17 17:41           ` Jeremy Fitzhardinge
2010-11-16 21:08 ` [PATCH 10/14] x86/pvticketlock: use callee-save for lock_spinning Jeremy Fitzhardinge
2010-11-16 21:08 ` [PATCH 11/14] x86/ticketlock: don't inline _spin_unlock when using paravirt spinlocks Jeremy Fitzhardinge
2010-11-16 21:08 ` [PATCH 12/14] x86/ticketlocks: when paravirtualizing ticket locks, increment by 2 Jeremy Fitzhardinge
2010-11-16 21:08 ` [PATCH 13/14] x86/ticketlock: add slowpath logic Jeremy Fitzhardinge
2010-11-17  8:31   ` Jan Beulich
2010-11-17  8:52     ` Jeremy Fitzhardinge
2010-11-17  8:56       ` Jeremy Fitzhardinge
2010-11-17  9:08         ` Jeremy Fitzhardinge
2010-11-17  9:34           ` Jan Beulich
2010-11-17  8:58       ` Avi Kivity
2010-11-17  9:05         ` Jeremy Fitzhardinge
2010-11-17  9:10           ` Avi Kivity
2010-11-17 12:21   ` Peter Zijlstra
2010-11-17 15:25     ` [Xen-devel] " Jeremy Fitzhardinge
2011-01-17 15:22   ` Srivatsa Vaddagiri [this message]
2011-01-19 16:23     ` Srivatsa Vaddagiri
2011-01-24 21:56       ` Jeremy Fitzhardinge
2011-02-18 17:03         ` Srivatsa Vaddagiri
2011-01-19 18:31     ` Jeremy Fitzhardinge
2011-01-19 18:39       ` Srivatsa Vaddagiri
2011-01-19 18:55         ` Jeremy Fitzhardinge
2011-01-20  4:28           ` Srivatsa Vaddagiri
2011-01-20  9:52           ` Jan Beulich
2010-11-16 21:08 ` [PATCH 14/14] x86/ticketlocks: tidy up __ticket_unlock_kick() Jeremy Fitzhardinge
2010-11-17  8:56 ` [PATCH 00/14] PV ticket locks without expanding spinlock Avi Kivity
2011-01-19 16:44 ` Srivatsa Vaddagiri
2011-01-19 17:07   ` [PATCH 1/3] debugfs: Add support to print u32 array Srivatsa Vaddagiri
2011-01-19 17:12   ` [PATCH 2/3] kvm hypervisor : Add hypercalls to support pv-ticketlock Srivatsa Vaddagiri
2011-01-19 17:21     ` Peter Zijlstra
2011-01-19 18:29       ` Srivatsa Vaddagiri
2011-01-19 18:53       ` Jeremy Fitzhardinge
2011-01-20 11:42         ` Srivatsa Vaddagiri
2011-01-20 17:49           ` Jeremy Fitzhardinge
2011-01-20 11:59         ` Srivatsa Vaddagiri
2011-01-20 13:41           ` Peter Zijlstra
2011-01-20 14:34             ` Srivatsa Vaddagiri
2011-01-20 17:56           ` Jeremy Fitzhardinge
2011-01-21 14:02             ` Srivatsa Vaddagiri
2011-01-21 14:48               ` Rik van Riel
2011-01-22  6:14                 ` Srivatsa Vaddagiri
2011-01-22 14:53                   ` Rik van Riel
2011-01-24 17:49                     ` Jeremy Fitzhardinge
2011-01-19 17:23     ` Srivatsa Vaddagiri
2011-01-19 17:50       ` Peter Zijlstra
2011-01-19 17:17   ` [PATCH 3/3] kvm guest : Add support for pv-ticketlocks Srivatsa Vaddagiri

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