Re: [KVM PATCH v10] kvm: add support for irqfd

Michael S. Tsirkin
2009-05-26T16:42:57Z

On Wed, May 20, 2009 at 10:30:49AM -0400, Gregory Haskins wrote:
> +static int
> +irqfd_wakeup(wait_queue_t *wait, unsigned mode, int sync, void *key)
> +{
> + struct _irqfd *irqfd = container_of(wait, struct _irqfd, wait);
> +
> + /*
> + * The wake_up is called with interrupts disabled. Therefore we need
> + * to defer the IRQ injection until later since we need to acquire the
> + * kvm->lock to do so.
> + */
> + schedule_work(&irqfd->work);
> +
> + return 0;
> +}

This schedule_work is there just to work around the spinlock
in eventfd_signal, which we don't really need. Isn't this right?
And this is on each interrupt. Seems like a pity.
How about a flag in eventfd that would
convert it from waking up someone to a plain function call?

Davide, could we add something like

diff --git a/fs/eventfd.c b/fs/eventfd.c
index 2a701d5..8bfa308 100644
--- a/fs/eventfd.c
+++ b/fs/eventfd.c
@@ -29,6 +29,7 @@ struct eventfd_ctx {
*/
__u64 count;
unsigned int flags;
+ int nolock;
};

/*
@@ -46,6 +47,12 @@ int eventfd_signal(struct file *file, int n)

if (n < 0)
return -EINVAL;
+ if (ctx->nolock) {
+ /* Whoever set nolock
+ better set wqh.func as well. */
+ ctx->wqh.func(&ctx->wqh, 0, 0, NULL);
+ return 0;
+ }
spin_lock_irqsave(&ctx->wqh.lock, flags);
if (ULLONG_MAX - ctx->count < n)
n = (int) (ULLONG_MAX - ctx->count);

--
MST