From: Jeremy Fitzhardinge <jeremy@goop.org>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Stephan Diestelhorst <stephan.diestelhorst@amd.com>,
"H. Peter Anvin" <hpa@zytor.com>, Jan Beulich <JBeulich@suse.com>,
Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>,
Ingo Molnar <mingo@elte.hu>, Andi Kleen <andi@firstfloor.org>,
Peter Zijlstra <peterz@infradead.org>,
Nick Piggin <npiggin@kernel.dk>,
the arch/x86 maintainers <x86@kernel.org>,
"xen-devel@lists.xensource.com" <xen-devel@lists.xensource.com>,
Avi Kivity <avi@redhat.com>,
Marcelo Tosatti <mtosatti@redhat.com>, KVM <kvm@vger.kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [Xen-devel] [PATCH 00/10] [PATCH RFC V2] Paravirtualized ticketlocks
Date: Wed, 28 Sep 2011 12:06:36 -0700 [thread overview]
Message-ID: <4E83703C.2010907@goop.org> (raw)
In-Reply-To: <CA+55aFwm7ESNfrHhEHrAKcjcPUq8YxtuEkJd5PzAekYo2dMYNw@mail.gmail.com>
On 09/28/2011 11:49 AM, Linus Torvalds wrote:
> But I don't care all *that* deeply. I do agree that the xaddw trick is
> pretty tricky. I just happen to think that it's actually *less* tricky
> than "read the upper bits separately and depend on subtle ordering
> issues with another writer that happens at the same time on another
> CPU".
>
> So I can live with either form - as long as it works. I think it might
> be easier to argue that the xaddw is guaranteed to work, because all
> values at all points are unarguably atomic (yeah, we read the lower
> bits nonatomically, but as the owner of the lock we know that nobody
> else can write them).
Exactly. I just did a locked add variant, and while the code looks a
little simpler, it definitely has more actual complexity to analyze.
J
next prev parent reply other threads:[~2011-09-28 19:06 UTC|newest]
Thread overview: 42+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-09-15 0:31 [PATCH 00/10] [PATCH RFC V2] Paravirtualized ticketlocks Jeremy Fitzhardinge
2011-09-15 0:31 ` [PATCH 01/10] x86/ticketlocks: remove obsolete comment Jeremy Fitzhardinge
2011-09-15 0:31 ` [PATCH 02/10] x86/spinlocks: replace pv spinlocks with pv ticketlocks Jeremy Fitzhardinge
2011-09-15 0:31 ` [PATCH 03/10] x86/ticketlock: don't inline _spin_unlock when using paravirt spinlocks Jeremy Fitzhardinge
2011-09-15 0:31 ` [PATCH 04/10] x86/ticketlock: collapse a layer of functions Jeremy Fitzhardinge
2011-09-15 0:31 ` [PATCH 05/10] xen/pvticketlock: Xen implementation for PV ticket locks Jeremy Fitzhardinge
2011-09-15 0:31 ` [PATCH 06/10] x86/pvticketlock: use callee-save for lock_spinning Jeremy Fitzhardinge
2011-09-15 0:31 ` [PATCH 07/10] x86/ticketlocks: when paravirtualizing ticket locks, increment by 2 Jeremy Fitzhardinge
2011-09-15 0:31 ` Jeremy Fitzhardinge
2011-09-15 0:31 ` [PATCH 08/10] x86/ticketlock: add slowpath logic Jeremy Fitzhardinge
2011-09-15 0:31 ` [PATCH 09/10] xen/pvticketlock: allow interrupts to be enabled while blocking Jeremy Fitzhardinge
2011-09-15 0:31 ` [PATCH 10/10] xen: enable PV ticketlocks on HVM Xen Jeremy Fitzhardinge
2011-09-27 9:34 ` [Xen-devel] [PATCH 00/10] [PATCH RFC V2] Paravirtualized ticketlocks Stephan Diestelhorst
2011-09-27 9:34 ` Stephan Diestelhorst
2011-09-27 9:34 ` Stephan Diestelhorst
2011-09-27 16:44 ` [Xen-devel] " Jeremy Fitzhardinge
2011-09-27 16:44 ` Jeremy Fitzhardinge
2011-09-28 13:58 ` [Xen-devel] " Stephan Diestelhorst
2011-09-28 16:44 ` Jeremy Fitzhardinge
2011-09-28 18:13 ` Stephan Diestelhorst
2011-09-28 15:38 ` Linus Torvalds
2011-09-28 15:55 ` Jan Beulich
2011-09-28 15:55 ` Jan Beulich
2011-09-28 16:10 ` Linus Torvalds
2011-09-28 16:47 ` Jeremy Fitzhardinge
2011-09-28 17:22 ` Linus Torvalds
2011-09-28 17:24 ` H. Peter Anvin
2011-09-28 17:50 ` Jeremy Fitzhardinge
2011-09-28 18:08 ` Stephan Diestelhorst
2011-09-28 18:27 ` Jeremy Fitzhardinge
2011-09-28 18:49 ` Linus Torvalds
2011-09-28 19:06 ` Jeremy Fitzhardinge [this message]
2011-10-06 14:04 ` Stephan Diestelhorst
2011-10-06 17:40 ` Jeremy Fitzhardinge
2011-10-06 18:09 ` Jeremy Fitzhardinge
2011-10-10 7:32 ` Ingo Molnar
2011-10-10 19:51 ` Jeremy Fitzhardinge
2011-10-10 11:00 ` Stephan Diestelhorst
2011-10-10 11:00 ` Stephan Diestelhorst
2011-10-10 14:01 ` Stephan Diestelhorst
2011-10-10 14:01 ` Stephan Diestelhorst
2011-10-10 19:44 ` Jeremy Fitzhardinge
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