Messages in this thread | | | Date | Wed, 19 Mar 2014 18:19:06 +0100 | From | Oleg Nesterov <> | Subject | Re: [PATCH RFC] sched: introduce add_wait_queue_exclusive_head |
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On 03/19, Peter Zijlstra wrote: > > On Wed, Mar 19, 2014 at 05:49:07PM +0100, Oleg Nesterov wrote: > > +static void add_wait_queue_flag(wait_queue_head_t *q, wait_queue_t *wait) > > +{ > > + struct list_head *head = &q->task_list; > > + wait_queue_t *excl; > > + > > + if (wait->flags & WQ_FLAG_EXCLUSIVE) { > > + if (wait->flags & WQ_FLAG_EXCLUSIVE_HEAD) { > > + list_for_each_entry(excl, head, task_list) > > + if (excl->flags & WQ_FLAG_EXCLUSIVE) { > > + head = &excl->task_list; > > + break; > > + } > > I prefer an extra pair of { } here,
OK,
> but the main concern would be the > cost of that iteration.
Yes.
This change assumes that we do not mix exclusive and !exclusive, in this case list_for_each_entry() is cheap, the list is either empty or the first entry is WQ_FLAG_EXCLUSIVE.
Otherwise the user should blame itself, but the code still will work correctly.
Or we can do
if (WQ_FLAG_EXCLUSIVE_HEAD) { WARN_ON(!list_empty(head) && (list_first_entry(...)-flags & WQ_FLAG_EXCLUSIVE)); ... }
> Other than that, yes something like that would do I suppose.
OK, I'll try to test/cleanup/resend tomorrow.
Oleg.
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