On Wed, Oct 21, 2009 at 10:34:53AM -0400, Gregory Haskins wrote:
> IRQFD currently uses a deferred workqueue item to execute the injection
> operation. It was originally designed this way because kvm_set_irq()
> required the caller to hold the irq_lock mutex, and the eventfd callback
> is invoked from within a non-preemptible critical section.
>
> With the advent of lockless injection support in kvm_set_irq, the deferment
> mechanism is no longer technically needed. Since context switching to the
> workqueue is a source of interrupt latency, lets switch to a direct
> method.
>
kvm_set_irq is fully lockless only in MSI case. IOAPIC/PIC has mutexes.
> Signed-off-by: Gregory Haskins <ghaskins@xxxxxxxxxx>
> ---
>
> virt/kvm/eventfd.c | 15 +++------------
> 1 files changed, 3 insertions(+), 12 deletions(-)
>
> diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
> index 30f70fd..1a529d4 100644
> --- a/virt/kvm/eventfd.c
> +++ b/virt/kvm/eventfd.c
> @@ -49,16 +49,14 @@ struct _irqfd {
> poll_table pt;
> wait_queue_head_t *wqh;
> wait_queue_t wait;
> - struct work_struct inject;
> struct work_struct shutdown;
> };
>
> static struct workqueue_struct *irqfd_cleanup_wq;
>
> static void
> -irqfd_inject(struct work_struct *work)
> +irqfd_inject(struct _irqfd *irqfd)
> {
> - struct _irqfd *irqfd = container_of(work, struct _irqfd, inject);
> struct kvm *kvm = irqfd->kvm;
>
> kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 1);
> @@ -80,12 +78,6 @@ irqfd_shutdown(struct work_struct *work)
> remove_wait_queue(irqfd->wqh, &irqfd->wait);
>
> /*
> - * We know no new events will be scheduled at this point, so block
> - * until all previously outstanding events have completed
> - */
> - flush_work(&irqfd->inject);
> -
> - /*
> * It is now safe to release the object's resources
> */
> eventfd_ctx_put(irqfd->eventfd);
> @@ -126,7 +118,7 @@ irqfd_wakeup(wait_queue_t *wait, unsigned mode, int sync, void *key)
>
> if (flags & POLLIN)
> /* An event has been signaled, inject an interrupt */
> - schedule_work(&irqfd->inject);
> + irqfd_inject(irqfd);
>
> if (flags & POLLHUP) {
> /* The eventfd is closing, detach from KVM */
> @@ -179,7 +171,6 @@ kvm_irqfd_assign(struct kvm *kvm, int fd, int gsi)
> irqfd->kvm = kvm;
> irqfd->gsi = gsi;
> INIT_LIST_HEAD(&irqfd->list);
> - INIT_WORK(&irqfd->inject, irqfd_inject);
> INIT_WORK(&irqfd->shutdown, irqfd_shutdown);
>
> file = eventfd_fget(fd);
> @@ -214,7 +205,7 @@ kvm_irqfd_assign(struct kvm *kvm, int fd, int gsi)
> * before we registered, and trigger it as if we didn't miss it.
> */
> if (events & POLLIN)
> - schedule_work(&irqfd->inject);
> + irqfd_inject(irqfd);
>
> /*
> * do not drop the file until the irqfd is fully initialized, otherwise
>
> --
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--
Gleb.
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