Messages in this thread | | | Date | Wed, 17 Feb 2016 22:10:02 +1100 | From | Dave Chinner <> | Subject | Re: [RFC PATCH 1/2] lib/percpu-list: Per-cpu list with associated per-cpu locks |
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On Wed, Feb 17, 2016 at 12:00:40PM +0100, Peter Zijlstra wrote: > On Wed, Feb 17, 2016 at 08:53:18PM +1100, Dave Chinner wrote: > > > +/** > > > + * for_all_percpu_list_entries - iterate over all the per-cpu list with locking > > > + * @pos: the type * to use as a loop cursor for the current . > > > + * @next: an internal type * variable pointing to the next entry > > > + * @pchead: an internal struct list * of percpu list head > > > + * @pclock: an internal variable for the current per-cpu spinlock > > > + * @head: the head of the per-cpu list > > > + * @member: the name of the per-cpu list within the struct > > > + */ > > > +#define for_all_percpu_list_entries(pos, next, pchead, pclock, head, member)\ > > > + { \ > > > + int cpu; \ > > > + for_each_possible_cpu (cpu) { \ > > > + typeof(*pos) *next; \ > > > + spinlock_t *pclock = per_cpu_ptr(&(head)->lock, cpu); \ > > > + struct list_head *pchead = &per_cpu_ptr(head, cpu)->list;\ > > > + spin_lock(pclock); \ > > > + list_for_each_entry_safe(pos, next, pchead, member.list) > > > + > > > +#define end_all_percpu_list_entries(pclock) spin_unlock(pclock); } } > > > > This is a bit of a landmine > > Yeah, that is pretty terrible. Maybe a visitor interface is advisable? > > visit_percpu_list_entries(struct percpu_list *head, void (*visitor)(struct list_head *pos, void *data), void *data) > { > int cpu; > > for_each_possible_cpu(cpu) { > spinlock_t *lock = per_cpu_ptr(&head->lock, cpu); > struct list_head *head = per_cpu_ptr(&head->list, cpu); > struct list_head *pos, *tmp; > > spin_lock(lock); > for (pos = head->next, tmp = pos->next; pos != head; pos = tmp) > visitor(pos, data);
I thought about this - it's the same problem as the list_lru walking functions. That is, the visitor has to be able to drop the list lock to do blocking operations, so the lock has to be passed to the visitor/internal loop context somehow, and the way the callers can use it need to be documented.
Cheers,
Dave. -- Dave Chinner david@fromorbit.com
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