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Groups > linux.kernel > #1260660
| From | Peter Zijlstra <peterz@infradead.org> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() |
| Date | 2015-11-02 15:00 +0100 |
| Message-ID | <qqnOr-5Zc-23@gated-at.bofh.it> (permalink) |
| References | <qqnOq-5Zc-11@gated-at.bofh.it> <qqnOq-5Zc-9@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Mon, Nov 02, 2015 at 02:29:05PM +0100, Peter Zijlstra wrote:
> Note that while smp_cond_acquire() has an explicit
> smp_read_barrier_depends() for Alpha, neither sites it gets used in
> were actually buggy on Alpha for their lack of it. The first uses
> smp_rmb(), which on Alpha is a full barrier too and therefore serves
> its purpose. The second had an explicit full barrier.
> +/**
> + * smp_cond_acquire() - Spin wait for cond with ACQUIRE ordering
> + * @cond: boolean expression to wait for
> + *
> + * Equivalent to using smp_load_acquire() on the condition variable but employs
> + * the control dependency of the wait to reduce the barrier on many platforms.
> + *
> + * The control dependency provides a LOAD->STORE order, the additional RMB
> + * provides LOAD->LOAD order, together they provide LOAD->{LOAD,STORE} order,
> + * aka. ACQUIRE.
> + */
> +#define smp_cond_acquire(cond) do { \
> + while (!(cond)) \
> + cpu_relax(); \
> + smp_read_barrier_depends(); /* ctrl */ \
> + smp_rmb(); /* ctrl + rmb := acquire */ \
> +} while (0)
So per the above argument we could leave out the
smp_read_barrier_depends() for Alpha, although that would break
consistency with all the other control dependency primitives we have. It
would avoid issuing a double barrier.
Thoughts?
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[PATCH 0/4] scheduler ordering bits Peter Zijlstra <peterz@infradead.org> - 2015-11-02 15:00 +0100
[PATCH 2/4] sched: Document Program-Order guarantees Peter Zijlstra <peterz@infradead.org> - 2015-11-02 15:00 +0100
Re: [PATCH 2/4] sched: Document Program-Order guarantees Paul Turner <pjt@google.com> - 2015-11-02 21:30 +0100
Re: [PATCH 2/4] sched: Document Program-Order guarantees Peter Zijlstra <peterz@infradead.org> - 2015-11-02 21:40 +0100
Re: [PATCH 2/4] sched: Document Program-Order guarantees Paul Turner <pjt@google.com> - 2015-11-02 23:10 +0100
Re: [PATCH 2/4] sched: Document Program-Order guarantees Peter Zijlstra <peterz@infradead.org> - 2015-11-02 23:20 +0100
[PATCH 4/4] locking: Introduce smp_cond_acquire() Peter Zijlstra <peterz@infradead.org> - 2015-11-02 15:00 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Peter Zijlstra <peterz@infradead.org> - 2015-11-02 15:00 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Will Deacon <will.deacon@arm.com> - 2015-11-02 18:50 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-11-03 02:20 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-03 02:30 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Will Deacon <will.deacon@arm.com> - 2015-11-02 18:50 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-02 19:10 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Will Deacon <will.deacon@arm.com> - 2015-11-02 19:40 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-02 20:20 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Will Deacon <will.deacon@arm.com> - 2015-11-02 21:00 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Peter Zijlstra <peterz@infradead.org> - 2015-11-02 21:30 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Peter Zijlstra <peterz@infradead.org> - 2015-11-02 23:00 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-11-03 03:00 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-03 20:50 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-11-04 05:00 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-04 05:50 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-11-04 14:10 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() David Howells <dhowells@redhat.com> - 2015-11-02 21:40 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Peter Zijlstra <peterz@infradead.org> - 2015-11-02 21:50 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-02 22:20 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Oleg Nesterov <oleg@redhat.com> - 2015-11-03 18:10 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Peter Zijlstra <peterz@infradead.org> - 2015-11-03 19:30 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Boqun Feng <boqun.feng@gmail.com> - 2015-11-11 10:50 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Boqun Feng <boqun.feng@gmail.com> - 2015-11-11 11:40 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Oleg Nesterov <oleg@redhat.com> - 2015-11-11 20:00 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-11-12 15:00 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Peter Zijlstra <peterz@infradead.org> - 2015-11-11 13:20 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Oleg Nesterov <oleg@redhat.com> - 2015-11-11 19:50 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-11 22:30 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Boqun Feng <boqun.feng@gmail.com> - 2015-11-12 08:20 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Peter Zijlstra <peterz@infradead.org> - 2015-11-12 11:30 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Oleg Nesterov <oleg@redhat.com> - 2015-11-12 15:10 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Boqun Feng <boqun.feng@gmail.com> - 2015-11-12 15:50 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-11-12 16:50 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Will Deacon <will.deacon@arm.com> - 2015-11-12 23:00 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-11-12 15:50 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Peter Zijlstra <peterz@infradead.org> - 2015-11-12 16:00 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-11-12 16:10 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Peter Zijlstra <peterz@infradead.org> - 2015-11-12 16:10 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-11-12 16:30 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Will Deacon <will.deacon@arm.com> - 2015-11-12 22:30 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Boqun Feng <boqun.feng@gmail.com> - 2015-11-12 16:20 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Oleg Nesterov <oleg@redhat.com> - 2015-11-12 18:50 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Peter Zijlstra <peterz@infradead.org> - 2015-11-12 19:10 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Oleg Nesterov <oleg@redhat.com> - 2015-11-12 19:40 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-11-12 20:00 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Will Deacon <will.deacon@arm.com> - 2015-11-12 22:40 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() "Paul E. McKenney" <paulmck@linux.vnet.ibm.com> - 2015-11-13 00:50 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Linus Torvalds <torvalds@linux-foundation.org> - 2015-11-12 19:30 +0100
Re: [PATCH 4/4] locking: Introduce smp_cond_acquire() Will Deacon <will.deacon@arm.com> - 2015-11-12 23:10 +0100
[PATCH 1/4] sched: Better document the try_to_wake_up() barriers Peter Zijlstra <peterz@infradead.org> - 2015-11-02 15:00 +0100
[PATCH 3/4] sched: Fix a race in try_to_wake_up() vs schedule() Peter Zijlstra <peterz@infradead.org> - 2015-11-02 15:00 +0100
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