Messages in this thread | | | From | Rusty Russell <> | Subject | Re: [PATCH] minor sched-E1 tweaks and questions | Date | Thu, 10 Jan 2002 14:48:42 +1100 |
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In message <Pine.LNX.4.33.0201091126520.2276-100000@localhost.localdomain> you write: > > Q. How can this happen in expire_task(): > > if (p->array != rq->active) { > > p->need_resched = 1; > > return; > > } > > if a task gets delayed by some really heavy IRQ load and the timer > interrupt hits the task twice.
Hmm... still don't see it. update_process_times() surely doesn't re-enter? And another CPU cannot load_balance() p (== current) away from us.
Another question:
if (likely(prev != next)) { rq->nr_switches++; rq->curr = next; next->cpu = prev->cpu; context_switch(prev, next); /* * The runqueue pointer might be from another CPU * if the new task was last running on a different * CPU - thus re-load it. */ barrier(); rq = this_rq(); } spin_unlock_irq(&rq->lock);
I do not understand this comment. How can rq (ie. smp_processor_id()) change? Nothing sleeps here, and if it DID change, the spin_unlock_irq() would be wrong...
> i've taken your fixes, please double-check the next patch whether all of > them are correctly applied.
Um, missed one:
static struct runqueue { - int cpu; spinlock_t lock; - unsigned long nr_running, nr_switches, last_rt_event; + unsigned long nr_running, nr_switches; task_t *curr, *idle; prio_array_t *active, *expired, arrays[2]; - char __pad [SMP_CACHE_BYTES]; + int prev_nr_running[NR_CPUS]; } runqueues [NR_CPUS] __cacheline_aligned;
You want each entry in the array to be aligned, not the whole array! You need to define the struct runqueue to be the cacheline aligned (using ____cacheline_aligned since it's a type), THEN put the __cacheline_aligned after the array declaration so it gets put in the aligned section:
struct runqueue { spinlock_t lock; unsigned long nr_running, nr_switches; task_t *curr, *idle; prio_array_t *active, *expired, arrays[2]; int prev_nr_running[NR_CPUS]; } ____cacheline_aligned;
static struct runqueue runqueues [NR_CPUS] __cacheline_aligned;
This is why my __per_cpu patch was invented 8) Cheers, Rusty. -- Anyone who quotes me in their sig is an idiot. -- Rusty Russell. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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