From: Andrew Haley <aph@redhat.com>
To: David Miller <davem@davemloft.net>
Cc: roland@hack.frob.com, maxim@codesourcery.com,
joseph@codesourcery.com, rdsandiford@googlemail.com,
libc-ports@sourceware.org, libc-alpha@sourceware.org
Subject: Re: [PATCH] Unify pthread_spin_[try]lock implementations.
Date: Wed, 11 Jul 2012 08:44:00 -0000 [thread overview]
Message-ID: <4FFD3CD9.4030206@redhat.com> (raw)
In-Reply-To: <20120711.012509.1325789838255235021.davem@davemloft.net>
On 07/11/2012 09:25 AM, David Miller wrote:
> From: Roland McGrath <roland@hack.frob.com>
> Date: Wed, 11 Jul 2012 01:14:41 -0700 (PDT)
>
>>> +int
>>> +pthread_spin_lock (pthread_spinlock_t *lock)
>>> +{
>>> + while (atomic_compare_and_exchange_val_acq (lock, 1, 0) != 0)
>>> + while (*lock != 0)
>>> + ;
>>
>> What's the inner loop for?
>
> I guess the idea is to spin with non-atomic reads when the lock is
> contended so we don't do expensive bus cycles grabbing the cache line
> in exclusive state over and over again.
>
> If we spun using only the atomic it would be very expensive.
Sure, but on ARM at least there's no guarantee that the local processor
will see changes to the state of the lock when another processor frees
it.
Andrew.
next prev parent reply other threads:[~2012-07-11 8:44 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-06-14 4:36 [PATCH 2/3, MIPS] Rewrite MIPS' pthread_spin_[try]lock using __atomic_* builtins Maxim Kuvyrkov
2012-06-28 23:10 ` Joseph S. Myers
2012-07-11 5:58 ` [PATCH] Unify pthread_spin_[try]lock implementations Maxim Kuvyrkov
2012-07-11 8:15 ` Roland McGrath
2012-07-11 8:25 ` David Miller
2012-07-11 8:44 ` Andrew Haley [this message]
2012-07-11 8:54 ` Maxim Kuvyrkov
2012-07-11 9:02 ` Andrew Haley
2012-07-11 9:05 ` Maxim Kuvyrkov
2012-07-11 11:22 ` Roland McGrath
2012-07-11 14:52 ` Chris Metcalf
2012-07-11 22:16 ` Maxim Kuvyrkov
2012-07-25 18:13 ` Roland McGrath
2012-07-25 19:04 ` Chris Metcalf
2012-07-25 20:22 ` Roland McGrath
2012-07-25 20:29 ` Chris Metcalf
2012-07-25 20:43 ` Roland McGrath
2012-08-15 3:17 ` Maxim Kuvyrkov
2012-08-15 16:27 ` Roland McGrath
2012-08-15 16:39 ` Maxim Kuvyrkov
2012-08-15 16:44 ` Roland McGrath
2012-08-15 16:53 ` Maxim Kuvyrkov
2012-08-15 16:56 ` Roland McGrath
2012-08-15 17:05 ` Maxim Kuvyrkov
2012-08-15 17:05 ` Jeff Law
2012-08-15 17:11 ` Roland McGrath
2012-08-15 17:24 ` Jeff Law
2012-08-15 16:40 ` Joseph S. Myers
2012-08-15 16:43 ` Carlos O'Donell
2012-08-15 22:00 ` Andreas Schwab
2012-08-16 10:21 ` Torvald Riegel
2012-08-16 12:40 ` Chris Metcalf
2012-08-22 23:16 ` Maxim Kuvyrkov
2012-07-11 8:26 ` Maxim Kuvyrkov
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