Re: [RFC PATCH] VFIO: Add a parameter to force nonthread IRQ
From: Paolo Bonzini
Date: Wed Oct 28 2015 - 14:29:12 EST
On 28/10/2015 18:50, Yunhong Jiang wrote:
> > No, I don't think you can use raw_spinlock there. The problem is not
> > just eventfd_signal, it is especially wake_up_locked_poll. You cannot
> > convert the whole workqueue infrastructure to use raw_spinlock.
> You mean the waitqueue, instead of workqueue, right?
> One choice is to change
> the eventfd to use simple wait queue, which is raw_spinlock. But use simple
> waitqueue on eventfd may in fact impact real time latency if not in this
Userspace can put an arbitrary amount of tasks on the work queue, so
it's not possible to use a simple wait queue. It would also touch
multiple subsystems, so it's much better to bypass the eventfd completely.
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