Messages in this thread | | | Subject | Re: [RFC PATCH 5/6] implement per-cpu&per-domain state machine call_srcu() | From | Peter Zijlstra <> | Date | Tue, 06 Mar 2012 12:52:14 +0100 |
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On Tue, 2012-03-06 at 17:57 +0800, Lai Jiangshan wrote: > +void srcu_barrier(struct srcu_struct *sp) > +{ > + struct srcu_sync sync; > + struct srcu_head *head = &sync.head; > + unsigned long chck_seq; /* snap */ > + > + int idle_loop = 0; > + int cpu; > + struct srcu_cpu_struct *scp; > + > + spin_lock_irq(&sp->gp_lock); > + chck_seq = sp->chck_seq; > + for_each_possible_cpu(cpu) {
ARGH!! this is really not ok.. so we spend all this time killing srcu_sync_expidited and co because they prod at all cpus for no good reason, and what do you do?
Also, what happens if your cpu isn't actually online?
> + scp = per_cpu_ptr(sp->srcu_per_cpu, cpu); > + if (scp->head && !safe_less_than(chck_seq, scp->head->chck_seq, > + sp->chck_seq)) { > + /* this path is likely enterred only once */ > + init_completion(&sync.completion); > + srcu_queue_callback(sp, scp, head, > + __synchronize_srcu_callback); > + /* don't need to wakeup the woken state machine */ > + spin_unlock_irq(&sp->gp_lock); > + wait_for_completion(&sync.completion); > + spin_lock_irq(&sp->gp_lock); > + } else { > + if ((++idle_loop & 0xF) == 0) { > + spin_unlock_irq(&sp->gp_lock); > + udelay(1); > + spin_lock_irq(&sp->gp_lock); > + }
The purpose of this bit isn't quite clear to me, is this simply a lock break?
> + } > + } > + spin_unlock_irq(&sp->gp_lock); > + > + flush_workqueue(srcu_callback_wq);
Since you already waited for the completions one by one, what's the purpose of this?
> +} > +EXPORT_SYMBOL_GPL(srcu_barrier);
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