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Groups > linux.kernel > #1263427
| From | Peter Zijlstra <peterz@infradead.org> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH tip/locking/core v9 2/6] locking/qspinlock: prefetch next node cacheline |
| Date | 2015-11-05 18:00 +0100 |
| Message-ID | <qrw3h-Mt-29@gated-at.bofh.it> (permalink) |
| References | <qprhn-3F0-1@gated-at.bofh.it> <qprhn-3F0-11@gated-at.bofh.it> <qqqjg-7AX-19@gated-at.bofh.it> <qqwf0-2M7-19@gated-at.bofh.it> <qrvTA-IK-23@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Thu, Nov 05, 2015 at 11:42:27AM -0500, Waiman Long wrote:
> If we observe next, we will observe val != tail sooner or later. It is not
> possible for it to clear the tail code in the lock. The tail xchg will
> guarantee that.
>
> Another alternative is to do something like
>
> + if (!next)
> while (!(next = READ_ONCE(node->next)))
> cpu_relax();
>
Yes maybe, although the main reason I fell over this was because it was
a separate change (and not mentioned in the Changelog).
Although the above would need braces (per CodingStyle), so:
if (!next) {
while (!(next = READ_ONCE(node->next)))
cpu_relax();
}
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Re: [PATCH tip/locking/core v9 2/6] locking/qspinlock: prefetch next node cacheline Peter Zijlstra <peterz@infradead.org> - 2015-11-02 17:40 +0100
Re: [PATCH tip/locking/core v9 2/6] locking/qspinlock: prefetch next node cacheline Peter Zijlstra <peterz@infradead.org> - 2015-11-03 00:00 +0100
Re: [PATCH tip/locking/core v9 2/6] locking/qspinlock: prefetch next node cacheline Waiman Long <waiman.long@hpe.com> - 2015-11-05 17:50 +0100
Re: [PATCH tip/locking/core v9 2/6] locking/qspinlock: prefetch next node cacheline Peter Zijlstra <peterz@infradead.org> - 2015-11-05 18:00 +0100
Re: [PATCH tip/locking/core v9 2/6] locking/qspinlock: prefetch next node cacheline Waiman Long <waiman.long@hpe.com> - 2015-11-05 17:10 +0100
Re: [PATCH tip/locking/core v9 2/6] locking/qspinlock: prefetch next node cacheline Peter Zijlstra <peterz@infradead.org> - 2015-11-05 17:40 +0100
Re: [PATCH tip/locking/core v9 2/6] locking/qspinlock: prefetch next node cacheline Waiman Long <waiman.long@hpe.com> - 2015-11-05 18:00 +0100
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