Gregory Haskins wrote: > Avi Kivity wrote: >> On 10/23/2009 04:38 AM, Gregory Haskins wrote: >>> Certain GSI's support lockless injecton, but we have no way to detect >>> which ones at the GSI level. Knowledge of this attribute will be >>> useful later in the series so that we can optimize irqfd injection >>> paths for cases where we know the code will not sleep. Therefore, >>> we provide an API to query a specific GSI. >>> >>> >> Instead of a lockless attribute, how about a ->set_atomic() method. For >> msi this can be the same as ->set(), for non-msi it can be a function >> that schedules the work (which will eventually call ->set()). >> >> The benefit is that we make a decision only once, when preparing the >> routing entry, and install that decision in the routing entry instead of >> making it again and again later. > > Yeah, I like this idea. I think we can also get rid of the custom > workqueue if we do this as well, TBD. So I looked into this. It isn't straight forward because you need to retain some kind of state across the deferment on a per-request basis (not per-GSI). Today, this state is neatly tracked into the irqfd object itself (e.g. it knows to toggle the GSI). So while generalizing this perhaps makes sense at some point, especially if irqfd-like interfaces get added, it probably doesn't make a ton of sense to expend energy on it ATM. It is basically a generalization of the irqfd deferrment code. Lets just wait until we have a user beyond irqfd for now. Sound acceptable? In the meantime, I found a bug in the irq_routing code, so I will submit a v3 with this fix, as well as a few other things I improved in the v2 series. Kind Regards, -Greg
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