On 07/23/2013 08:37 PM, Gleb Natapov wrote:
On Mon, Jul 22, 2013 at 11:50:16AM +0530, Raghavendra K T wrote:
+static void kvm_lock_spinning(struct arch_spinlock *lock, __ticket_t want)
[...]
+
+ /*
+ * halt until it's our turn and kicked. Note that we do safe halt
+ * for irq enabled case to avoid hang when lock info is overwritten
+ * in irq spinlock slowpath and no spurious interrupt occur to save us.
+ */
+ if (arch_irqs_disabled_flags(flags))
+ halt();
+ else
+ safe_halt();
+
+out:
So here now interrupts can be either disabled or enabled. Previous
version disabled interrupts here, so are we sure it is safe to have them
enabled at this point? I do not see any problem yet, will keep thinking.
If we enable interrupt here, then
+ cpumask_clear_cpu(cpu, &waiting_cpus);
and if we start serving lock for an interrupt that came here,
cpumask clear and w->lock=null may not happen atomically.
if irq spinlock does not take slow path we would have non null value for
lock, but with no information in waitingcpu.
I am still thinking what would be problem with that.
+ w->lock = NULL;
+ local_irq_restore(flags);
+ spin_time_accum_blocked(start);
+}
+PV_CALLEE_SAVE_REGS_THUNK(kvm_lock_spinning);
+
+/* Kick vcpu waiting on @lock->head to reach value @ticket */
+static void kvm_unlock_kick(struct arch_spinlock *lock, __ticket_t ticket)
+{
+ int cpu;
+
+ add_stats(RELEASED_SLOW, 1);
+ for_each_cpu(cpu, &waiting_cpus) {
+ const struct kvm_lock_waiting *w = &per_cpu(lock_waiting, cpu);
+ if (ACCESS_ONCE(w->lock) == lock &&
+ ACCESS_ONCE(w->want) == ticket) {
+ add_stats(RELEASED_SLOW_KICKED, 1);
+ kvm_kick_cpu(cpu);
What about using NMI to wake sleepers? I think it was discussed, but
forgot why it was dismissed.
I think I have missed that discussion. 'll go back and check. so what is
the idea here? we can easily wake up the halted vcpus that have
interrupt disabled?
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