On Fri, Nov 01, 2013 at 01:44:24PM +0000, Mel Gorman wrote:
> Ok, I see your point now but still wonder if this is too specialised
> for what we are trying to do. Could it have been done with a read-write
> semaphore with the global stop_cpus taking it for write and stop_two_cpus
> taking it for read?
rwsem for read is still global state.. That said it should be fairly
easy to use lglock for this.
Or write it with spinlocks like:
DEFINE_PER_CPU(spinlock_t, local_lock);
DEFINE_PER_CPU(int, have_global);
spinlock_t global_lock;
void local_lock(void)
{
preempt_disable();
spin_lock(this_cpu_ptr(&local_lock));
if (spin_is_locked(&global_lock)) {
spin_unlock(this_cpu_ptr(&local_lock));
spin_lock(&global_lock);
this_cpu_write(have_global, true);
spin_lock(this_cpu_ptr(&local_lock));
}
}
void local_unlock(void)
{
spin_unlock(this_cpu_ptr(&local_lock));
if (this_cpu_read(have_global)) {
this_cpu_write(have_global, false);
spin_unlock(&global_lock);
}
}
void global_lock(void)
{
int cpu;
spin_lock(&global_lock);
for_each_possible_cpu(cpu)
spin_unlock_wait(&per_cpu(local_lock, cpu));
}
void global_unlock(void)
{
spin_unlock(&global_lock);
}
Or possibly make the global_lock a mutex, plenty variants possible.
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