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    SubjectRe: [KVM PATCH v10] kvm: add support for irqfd
    On Tue, 26 May 2009, Michael S. Tsirkin wrote:

    > 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

    I'm sorry, but it's not very pretty. Please find another way around.



    > 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);



    - Davide




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