Re: [PATCH 1/4] Move irq routing data structure to rcu locking

Gleb Natapov
2009-07-13T13:25:10Z

On Mon, Jul 13, 2009 at 09:16:47AM -0400, Gregory Haskins wrote:
> Gleb Natapov wrote:
> > On Mon, Jul 13, 2009 at 09:01:33AM -0400, Gregory Haskins wrote:
> >
> >> Gleb Natapov wrote:
> >>
> >>> Signed-off-by: Gleb Natapov <gleb@redhat.com>
> >>> ---
> >>> include/linux/kvm_host.h | 2 +-
> >>> virt/kvm/irq_comm.c | 55 +++++++++++++++++++++-------------------------
> >>> virt/kvm/kvm_main.c | 1 -
> >>> 3 files changed, 26 insertions(+), 32 deletions(-)
> >>>
> >>> diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
> >>> index f54a0d3..6756b3e 100644
> >>> --- a/include/linux/kvm_host.h
> >>> +++ b/include/linux/kvm_host.h
> >>> @@ -161,7 +161,7 @@ struct kvm {
> >>>
> >>> struct mutex irq_lock;
> >>> #ifdef CONFIG_HAVE_KVM_IRQCHIP
> >>> - struct list_head irq_routing; /* of kvm_kernel_irq_routing_entry */
> >>> + struct kvm_kernel_irq_routing_entry *irq_routing;
> >>> struct hlist_head mask_notifier_list;
> >>> #endif
> >>>
> >>> diff --git a/virt/kvm/irq_comm.c b/virt/kvm/irq_comm.c
> >>> index 7af18b8..b2fa3f6 100644
> >>> --- a/virt/kvm/irq_comm.c
> >>> +++ b/virt/kvm/irq_comm.c
> >>> @@ -148,7 +148,8 @@ int kvm_set_irq(struct kvm *kvm, int irq_source_id, int irq, int level)
> >>> * IOAPIC. So set the bit in both. The guest will ignore
> >>> * writes to the unused one.
> >>> */
> >>> - list_for_each_entry(e, &kvm->irq_routing, link)
> >>> + rcu_read_lock();
> >>> + for (e = rcu_dereference(kvm->irq_routing); e && e->set; e++) {
> >>>
> >>>
> >> Hi Gleb,
> >> I haven't had a chance to fully digest and review these patches, but
> >> one thing I did notice is that you seem to be converting from a list to
> >> an open-coded structure. I am just curious why you made this design
> >> decision instead of using the RCU variant of list?
> >>
> >>
> > It is not scary "open-coded structure" it's just an array :) As I responded
> > to Michael the idea is to move msis out of irq_routing, make the array
> > much smaller and either use gsi as an index in the array or use hash table
> > instead looping over all entries. For now I can justify array as more
> > cache friendly data structure as we scan it linearly.
> >
>
> Ok, but that might be a good thing to mention in the patch header ;)
>
What exactly? Besides this is just an RFC. By the time it will be
applied (if at all) I may do the change already :)

> Kind Regards,
> -Greg
>
> >
> >> Regards,
> >> -Greg
> >>
> >>
> >>> if (e->gsi == irq) {
> >>> int r = e->set(e, kvm, sig_level);
> >>> if (r < 0)
> >>> @@ -156,6 +157,8 @@ int kvm_set_irq(struct kvm *kvm, int irq_source_id, int irq, int level)
> >>>
> >>> ret = r + ((ret < 0) ? 0 : ret);
> >>> }
> >>> + }
> >>> + rcu_read_unlock();
> >>> return ret;
> >>> }
> >>>
> >>> @@ -168,12 +171,15 @@ void kvm_notify_acked_irq(struct kvm *kvm, unsigned irqchip, unsigned pin)
> >>>
> >>> trace_kvm_ack_irq(irqchip, pin);
> >>>
> >>> - list_for_each_entry(e, &kvm->irq_routing, link)
> >>> + rcu_read_lock();
> >>> + for (e = rcu_dereference(kvm->irq_routing); e && e->set; e++) {
> >>> if (e->irqchip.irqchip == irqchip &&
> >>> e->irqchip.pin == pin) {
> >>> gsi = e->gsi;
> >>> break;
> >>> }
> >>> + }
> >>> + rcu_read_unlock();
> >>>
> >>> hlist_for_each_entry(kian, n, &kvm->arch.irq_ack_notifier_list, link)
> >>> if (kian->gsi == gsi)
> >>> @@ -264,19 +270,11 @@ void kvm_fire_mask_notifiers(struct kvm *kvm, int irq, bool mask)
> >>> kimn->func(kimn, mask);
> >>> }
> >>>
> >>> -static void __kvm_free_irq_routing(struct list_head *irq_routing)
> >>> -{
> >>> - struct kvm_kernel_irq_routing_entry *e, *n;
> >>> -
> >>> - list_for_each_entry_safe(e, n, irq_routing, link)
> >>> - kfree(e);
> >>> -}
> >>> -
> >>> void kvm_free_irq_routing(struct kvm *kvm)
> >>> {
> >>> - mutex_lock(&kvm->irq_lock);
> >>> - __kvm_free_irq_routing(&kvm->irq_routing);
> >>> - mutex_unlock(&kvm->irq_lock);
> >>> + /* Called only during vm destruction. Nobody can use the pointer
> >>> + at this stage */
> >>> + kfree(kvm->irq_routing);
> >>> }
> >>>
> >>> static int setup_routing_entry(struct kvm_kernel_irq_routing_entry *e,
> >>> @@ -326,43 +324,40 @@ int kvm_set_irq_routing(struct kvm *kvm,
> >>> unsigned nr,
> >>> unsigned flags)
> >>> {
> >>> - struct list_head irq_list = LIST_HEAD_INIT(irq_list);
> >>> - struct list_head tmp = LIST_HEAD_INIT(tmp);
> >>> - struct kvm_kernel_irq_routing_entry *e = NULL;
> >>> + struct kvm_kernel_irq_routing_entry *new, *old;
> >>> unsigned i;
> >>> int r;
> >>>
> >>> + /* last element is left zeroed and indicates the end of the array */
> >>> + new = kzalloc(sizeof(*new) * (nr + 1), GFP_KERNEL);
> >>> +
> >>> + if (!new)
> >>> + return -ENOMEM;
> >>> +
> >>> for (i = 0; i < nr; ++i) {
> >>> r = -EINVAL;
> >>> if (ue->gsi >= KVM_MAX_IRQ_ROUTES)
> >>> goto out;
> >>> if (ue->flags)
> >>> goto out;
> >>> - r = -ENOMEM;
> >>> - e = kzalloc(sizeof(*e), GFP_KERNEL);
> >>> - if (!e)
> >>> - goto out;
> >>> - r = setup_routing_entry(e, ue);
> >>> + r = setup_routing_entry(new + i, ue);
> >>> if (r)
> >>> goto out;
> >>> ++ue;
> >>> - list_add(&e->link, &irq_list);
> >>> - e = NULL;
> >>> }
> >>>
> >>> mutex_lock(&kvm->irq_lock);
> >>> - list_splice(&kvm->irq_routing, &tmp);
> >>> - INIT_LIST_HEAD(&kvm->irq_routing);
> >>> - list_splice(&irq_list, &kvm->irq_routing);
> >>> - INIT_LIST_HEAD(&irq_list);
> >>> - list_splice(&tmp, &irq_list);
> >>> + old = kvm->irq_routing;
> >>> + rcu_assign_pointer(kvm->irq_routing, new);
> >>> mutex_unlock(&kvm->irq_lock);
> >>>
> >>> + synchronize_rcu();
> >>> +
> >>> r = 0;
> >>> + new = old;
> >>>
> >>> out:
> >>> - kfree(e);
> >>> - __kvm_free_irq_routing(&irq_list);
> >>> + kfree(new);
> >>> return r;
> >>> }
> >>>
> >>> diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
> >>> index cf20dc1..24013b4 100644
> >>> --- a/virt/kvm/kvm_main.c
> >>> +++ b/virt/kvm/kvm_main.c
> >>> @@ -945,7 +945,6 @@ static struct kvm *kvm_create_vm(void)
> >>> if (IS_ERR(kvm))
> >>> goto out;
> >>> #ifdef CONFIG_HAVE_KVM_IRQCHIP
> >>> - INIT_LIST_HEAD(&kvm->irq_routing);
> >>> INIT_HLIST_HEAD(&kvm->mask_notifier_list);
> >>> #endif
> >>>
> >>>
> >>>
> >>
> >
> >
> >
> > --
> > Gleb.
> > --
> > To unsubscribe from this list: send the line "unsubscribe kvm" in
> > the body of a message to majordomo@vger.kernel.org
> > More majordomo info at http://vger.kernel.org/majordomo-info.html
> >
>
>

--
Gleb.