(2012/06/27 6:37), Andrew Morton wrote:
https://bugzilla.kernel.org/show_bug.cgi?id=43811
lru_add_drain_all() uses schedule_on_each_cpu(). But
schedule_on_each_cpu() hangs if a realtime thread is spinning, pinned
to a CPU. There's no intention to change the scheduler behaviour, so I
think we should remove schedule_on_each_cpu() from the kernel.
The biggest user of schedule_on_each_cpu() is lru_add_drain_all().
Does anyone have any thoughts on how we can do this? The obvious
approach is to declare these:
static DEFINE_PER_CPU(struct pagevec[NR_LRU_LISTS], lru_add_pvecs);
static DEFINE_PER_CPU(struct pagevec, lru_rotate_pvecs);
static DEFINE_PER_CPU(struct pagevec, lru_deactivate_pvecs);
to be irq-safe and use on_each_cpu(). lru_rotate_pvecs is already
irq-safe and converting lru_add_pvecs and lru_deactivate_pvecs looks
pretty simple.
Thoughts?
How about this kind of RCU synchronization ?
==
/*
* Double buffered pagevec for quick drain.
* The usual per-cpu-pvec user need to take rcu_read_lock() before accessing.
* External drainer of pvecs will relpace pvec vector and call synchroize_rcu(),
* and drain all pages on unused pvecs in turn.
*/
static DEFINE_PER_CPU(struct pagevec[NR_LRU_LISTS * 2], lru_pvecs);
atomic_t pvec_idx; /* must be placed onto some aligned address...*/
struct pagevec *my_pagevec(enum lru)
{
return pvec = &__get_cpu_var(lru_pvecs[lru << atomic_read(pvec_idx)]);
}
/*
* percpu pagevec access should be surrounded by these calls.
*/
static inline void pagevec_start_access()
{
rcu_read_lock();
}
static inline void pagevec_end_access()
{
rcu_read_unlock();
}
/*
* changing pagevec array vec 0 <-> 1
*/
static void lru_pvec_update()
{
if (atomic_read(&pvec_idx))
atomic_set(&pvec_idx, 0);
else
atomic_set(&pvec_idx, 1);
}
/*
* drain all LRUS on per-cpu pagevecs.
*/
DEFINE_MUTEX(lru_add_drain_all_mutex);
static void lru_add_drain_all()
{
mutex_lock(&lru_add_drain_mutex);
lru_pvec_update();
synchronize_rcu(); /* waits for all accessors to pvec quits. */
for_each_cpu(cpu)
drain_pvec_of_the_cpu(cpu);
mutex_unlock(&lru_add_drain_mutex);
}
==
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