From mboxrd@z Thu Jan  1 00:00:00 1970
From: Gleb Natapov <gleb@redhat.com>
Subject: Re: assign-dev: Purpose of interrupt_work
Date: Mon, 12 Oct 2009 11:42:43 +0200
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Cc: Jan Kiszka <jan.kiszka@web.de>, kvm-devel <kvm@vger.kernel.org>
To: Avi Kivity <avi@redhat.com>
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On Mon, Oct 12, 2009 at 11:40:59AM +0200, Avi Kivity wrote:
> On 10/12/2009 11:38 AM, Gleb Natapov wrote:
> >
> >>irqfd can work from interrupt context, so if we only use the
> >>workqueue for the many-vcpu cases, we should be fine.
> >>
> >>I think we can do it cleanly, too: in ioapic code, if we're talking
> >>to one vcpu, wake it immediately; otherwise schedule work to
> >>continue in process context.  This was the common code can always
> >>work in interrupt context and not worry about the work queue.
> >>
> >Even if we are talking to one cpu locking is still needed, so unless we
> >make it spinlock we can't inject from irq context. If we change mutex to
> >spinlock what is the point of work queue?
> 
> Not to loop over 4096 vcpus with interrupts disabled, triggered by
> guest action.
> 
But in a work queue you'll do this anyway. You can't access ioapic
without the lock.

--
			Gleb.