From: Jeremy Fitzhardinge <jeremy@goop.org>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Jan Beulich <JBeulich@novell.com>,
Peter Zijlstra <peterz@infradead.org>,
Xen-devel <xen-devel@lists.xensource.com>,
Avi Kivity <avi@redhat.com>, Nick Piggin <npiggin@suse.de>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH RFC 02/12] x86/ticketlock: convert spin loop to C
Date: Fri, 06 Aug 2010 13:33:41 -0700 [thread overview]
Message-ID: <4C5C71A5.3050500@goop.org> (raw)
In-Reply-To: <4C5C6DCE.4020206@zytor.com>
On 08/06/2010 01:17 PM, H. Peter Anvin wrote:
> On 08/06/2010 07:53 AM, Jeremy Fitzhardinge wrote:
>> On 08/06/2010 05:43 AM, Jan Beulich wrote:
>>> You certainly mean "the compiler currently treats this as being:" - I
>>> don't think there's a guarantee it'll always be doing so.
>>>
>>>> for (;;) {
>>>> if (inc.tickets.head == inc.tickets.tail)
>>>> goto out;
>>>> ...
>>>> }
>>>> out: barrier();
>>>> }
>>>>
>>>> (Which would probably be a reasonable way to clarify the code.)
>>> I therefore think it needs to be written this way.
>>
>> Agreed.
>>
>
> A call/return to an actual out-of-line function is a barrier (and will
> always be a barrier, as it is the fundamental ABI sequence points),
> but to an inline function it is not.
Yes. So the goto explicitly puts the barrier into the control flow which
should stop the compiler from doing anything unexpected.
J
WARNING: multiple messages have this Message-ID (diff)
From: Jeremy Fitzhardinge <jeremy@goop.org>
To: "H. Peter Anvin" <hpa@zytor.com>
Cc: Nick Piggin <npiggin@suse.de>,
Xen-devel <xen-devel@lists.xensource.com>,
Peter Zijlstra <peterz@infradead.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Jan Beulich <JBeulich@novell.com>, Avi Kivity <avi@redhat.com>
Subject: Re: [PATCH RFC 02/12] x86/ticketlock: convert spin loop to C
Date: Fri, 06 Aug 2010 13:33:41 -0700 [thread overview]
Message-ID: <4C5C71A5.3050500@goop.org> (raw)
In-Reply-To: <4C5C6DCE.4020206@zytor.com>
On 08/06/2010 01:17 PM, H. Peter Anvin wrote:
> On 08/06/2010 07:53 AM, Jeremy Fitzhardinge wrote:
>> On 08/06/2010 05:43 AM, Jan Beulich wrote:
>>> You certainly mean "the compiler currently treats this as being:" - I
>>> don't think there's a guarantee it'll always be doing so.
>>>
>>>> for (;;) {
>>>> if (inc.tickets.head == inc.tickets.tail)
>>>> goto out;
>>>> ...
>>>> }
>>>> out: barrier();
>>>> }
>>>>
>>>> (Which would probably be a reasonable way to clarify the code.)
>>> I therefore think it needs to be written this way.
>>
>> Agreed.
>>
>
> A call/return to an actual out-of-line function is a barrier (and will
> always be a barrier, as it is the fundamental ABI sequence points),
> but to an inline function it is not.
Yes. So the goto explicitly puts the barrier into the control flow which
should stop the compiler from doing anything unexpected.
J
next prev parent reply other threads:[~2010-08-06 20:33 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-07-17 1:03 [PATCH RFC 00/12] X86 ticket lock cleanups and improvements Jeremy Fitzhardinge
2010-07-17 1:03 ` [PATCH RFC 05/12] x86/ticketlock: make __ticket_spin_lock common Jeremy Fitzhardinge
2010-07-17 1:03 ` [PATCH RFC 07/12] x86/spinlocks: replace pv spinlocks with pv ticketlocks Jeremy Fitzhardinge
2010-07-17 1:03 ` [PATCH RFC 03/12] x86/ticketlock: Use C for __ticket_spin_unlock Jeremy Fitzhardinge
2010-07-20 15:38 ` [Xen-devel] " Konrad Rzeszutek Wilk
2010-07-20 15:38 ` Konrad Rzeszutek Wilk
2010-07-20 16:17 ` [Xen-devel] " Jeremy Fitzhardinge
2010-07-20 16:17 ` Jeremy Fitzhardinge
2010-08-06 17:47 ` [Xen-devel] " H. Peter Anvin
2010-08-06 17:47 ` H. Peter Anvin
2010-08-06 20:03 ` [Xen-devel] " Jeremy Fitzhardinge
2010-08-06 20:03 ` Jeremy Fitzhardinge
2010-07-17 1:03 ` [PATCH RFC 09/12] xen/pvticketlock: Xen implementation for PV ticket locks Jeremy Fitzhardinge
2010-09-26 11:39 ` Srivatsa Vaddagiri
2010-09-26 22:34 ` Jeremy Fitzhardinge
2010-09-26 22:34 ` Jeremy Fitzhardinge
2011-01-18 16:27 ` Srivatsa Vaddagiri
2011-01-19 1:28 ` Jeremy Fitzhardinge
2010-07-17 1:03 ` [PATCH RFC 10/12] x86/pvticketlock: keep count of blocked cpus Jeremy Fitzhardinge
2010-08-03 8:32 ` Peter Zijlstra
2010-08-03 8:32 ` Peter Zijlstra
2010-08-03 9:44 ` Nick Piggin
2010-08-03 15:45 ` Jeremy Fitzhardinge
2010-08-03 15:45 ` Jeremy Fitzhardinge
2010-07-17 1:03 ` [PATCH RFC 01/12] x86/ticketlock: clean up types and accessors Jeremy Fitzhardinge
2010-07-17 1:03 ` [PATCH RFC 11/12] x86/pvticketlock: use callee-save for lock_spinning Jeremy Fitzhardinge
2010-07-17 1:03 ` [PATCH RFC 04/12] x86/ticketlock: make large and small ticket versions of spin_lock the same Jeremy Fitzhardinge
2010-07-17 1:03 ` [PATCH RFC 06/12] x86/ticketlock: make __ticket_spin_trylock common Jeremy Fitzhardinge
2010-07-17 1:03 ` [PATCH RFC 02/12] x86/ticketlock: convert spin loop to C Jeremy Fitzhardinge
2010-08-02 15:07 ` Peter Zijlstra
2010-08-02 15:17 ` Jeremy Fitzhardinge
2010-08-02 15:17 ` Jeremy Fitzhardinge
2010-08-06 12:43 ` Jan Beulich
2010-08-06 14:53 ` Jeremy Fitzhardinge
2010-08-06 20:17 ` H. Peter Anvin
2010-08-06 20:17 ` H. Peter Anvin
2010-08-06 20:33 ` Jeremy Fitzhardinge [this message]
2010-08-06 20:33 ` Jeremy Fitzhardinge
2010-08-06 21:09 ` H. Peter Anvin
2010-08-06 21:09 ` H. Peter Anvin
2010-08-06 22:03 ` Jeremy Fitzhardinge
2010-07-17 1:03 ` [PATCH RFC 08/12] x86/ticketlock: collapse a layer of functions Jeremy Fitzhardinge
2010-07-17 1:03 ` [PATCH RFC 12/12] x86/pvticketlock: use callee-save for unlock_kick as well Jeremy Fitzhardinge
-- strict thread matches above, loose matches on Subject: below --
2010-07-03 0:06 [PATCH RFC 02/12] x86/ticketlock: convert spin loop to C Jeremy Fitzhardinge
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