Hello, On Thu, Sep 26, 2013 at 09:46:46AM +0200, Alexander Gordeev wrote: > > Can you please go into a bit of detail on that? Why does it matter? > > Because otherwise we will re-introduce a problem described by Michael: > "We have a small number of MSIs available, limited by hardware & > firmware, if we don't impose a quota then the first device that probes > will get most/all of the MSIs and other devices miss out." Still not following. Why wouldn't just letting the drivers request the optimal number they want and falling back to single interrupt mode work? ie. why can't we just have an all or nothing interface? > > Is it because you're worried you might cause performance regression by > > forcing prevoius partial multiple allocations to single interrupt > > operation? > > Well, not really. I think it won't be possible to force people not to use > partial allocations anyway. Some controllers just do not care how many MSIs > they are configured with. Some drivers derive the number of MSIs desired > from the number of CPUs online - in such cases allocating more MSIs (i.e. > a number the controller advertised) could cause a performance degradation > even. Yeah, sure thing but just let the *driver* decide that number without worrying about how many they can actually get. Ultimately, what we want is removing this extra variable which can arbitrarily affect the number of allocated interrupts so that we only have to worry about either proper multiple MSI mode or single interrupt mode, not something random inbetween. It is possible that there exists a driver which absolutely requires partial allocation on certain archs, but that should be a very special case and the interface should look accordingly ugly / special. But do we actually have those? Thanks. -- tejun -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
