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

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Aug 13, 2012 at 01:31:36PM +0300, Avi Kivity wrote:
> On 08/13/2012 01:24 PM, Gleb Natapov wrote:
> > 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.
> 
> Should be sized N * vcpus, where N is several dozen (generous amount of
> non-device vectors, though multicast will break it since it's
> essentially random).

KVM_MAX_VCPUS is 256 multiply by what? 50? this is 10K already.
You can not allocate that much in a single chunk, right?

> 
> 
> -- 
> error compiling committee.c: too many arguments to function