From: "H. Peter Anvin" <hpa@zytor.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Jeremy Fitzhardinge <jeremy@goop.org>,
Jan Beulich <JBeulich@suse.com>,
Stephan Diestelhorst <stephan.diestelhorst@amd.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, 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 10:24:33 -0700 [thread overview]
Message-ID: <4E835851.7070502@zytor.com> (raw)
In-Reply-To: <CA+55aFzGZp8YaQMMUMwV+pd_vnqR14CtiTmTtkXuotQBg0zspg@mail.gmail.com>
On 09/28/2011 10:22 AM, Linus Torvalds wrote:
> On Wed, Sep 28, 2011 at 9:47 AM, Jeremy Fitzhardinge <jeremy@goop.org> wrote:
>>
>> Could do something like:
>>
>> if (ticket->head >= 254)
>> prev = xadd(&ticket->head_tail, 0xff02);
>> else
>> prev = xadd(&ticket->head_tail, 0x0002);
>>
>> to compensate for the overflow.
>
> Oh wow. You havge an even more twisted mind than I do.
>
> I guess that will work, exactly because we control "head" and thus can
> know about the overflow in the low byte. But boy is that ugly ;)
>
> But at least you wouldn't need to do the loop with cmpxchg. So it's
> twisted and ugly, but migth be practical.
>
I suspect it should be coded as -254 in order to use a short immediate
if that is even possible...
-hpa
--
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel. I don't speak on their behalf.
next prev parent reply other threads:[~2011-09-28 17:31 UTC|newest]
Thread overview: 35+ 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 ` [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 16:44 ` Jeremy Fitzhardinge
2011-09-28 13:58 ` 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 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 [this message]
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
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 14:01 ` Stephan Diestelhorst
2011-10-10 19:44 ` Jeremy Fitzhardinge
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