Re: [RFC PATCH 0/2] irq destination caching prototype

[Gleb Natapov <gleb@redhat.com>]

On Mon, Aug 13, 2012 at 01:21:33PM +0300, Avi Kivity wrote:
> On 08/13/2012 01:16 PM, Gleb Natapov wrote:
> > On Mon, Aug 13, 2012 at 01:12:46PM +0300, Michael S. Tsirkin wrote:
> >> On Mon, Aug 13, 2012 at 12:36:41PM +0300, Avi Kivity wrote:
> >> > On 08/13/2012 12:16 PM, Gleb Natapov wrote:
> >> > > Here is a quick prototype of what we discussed yesterday. This one
> >> > > caches only MSI interrupts for now. The obvious problem is that not
> >> > > all interrupts (namely IPIs and MSIs using KVM_CAP_SIGNAL_MSI) use irq
> >> > > routing table, so they cannot be cached.
> >> > 
> >> > We can have a small rcu-managed hash table to look those up.
> >> 
> >> Yes but how small? We probably need at least one entry
> >> per vcpu, no?
> >> 
> > One entry? We will spend more time managing it than injecting interrupts
> > :) ideally we need entry for each IPI sent and for each potential MSI
> > from userspace. What happens when hash table is full? 
> 
> Drop the entire cache.
> 
OK. Then it should be big enough to not do it frequently.

> > We stop caching or
> > invalidate old entries? If later then cache can go valid->invalid which
> > may complicate the code.
> > 
> 
> We can drop the entire cache via rcu freeing.  In fact we can have a
> closed hash allocated as a single blob, easy to manage.
> 
That's what I am locking at doing, yes.

--
			Gleb.