On Sun, Oct 09, 2016 at 09:23:58PM +0200, Thomas Gleixner wrote: > On Sun, 9 Oct 2016, Rich Felker wrote: > > On Sun, Oct 09, 2016 at 01:03:10PM +0200, Thomas Gleixner wrote: > > My preference would just be to keep the branch, but with your improved > > version that doesn't need a function call: > > > > irqd_is_per_cpu(irq_desc_get_irq_data(desc)) > > > > While there is some overhead testing this condition every time, I can > > probably come up with several better places to look for a ~10 cycle > > improvement in the irq code path without imposing new requirements on > > the DT bindings. > > Fair enough. Your call. > > > As noted in my followup to the clocksource stall thread, there's also > > a possibility that it might make sense to consider the current > > behavior of having non-percpu irqs bound to a particular cpu as part > > of what's required by the compatible tag, in which case > > handle_percpu_irq or something similar/equivalent might be suitable > > for both the percpu and non-percpu cases. I don't understand the irq > > subsystem well enough to insist on that but I think it's worth > > consideration since it looks like it would improve performance of > > non-percpu interrupts a bit. > > Well, you can use handle_percpu_irq() for your device interrupts if you > guarantee at the hardware level that there is no reentrancy. Once you make > the hardware capable of delivering them on either core the picture changes.
One more concern here -- I see that handle_simple_irq is handling the soft-disable / IRQS_PENDING flag behavior, and irq_check_poll stuff that's perhaps important too. Since soft-disable is all we have (there's no hard-disable of interrupts), is this a problem? In other words, can drivers have an expectation of not receiving interrupts when the irq is disabled? I would think anything compatible with irq sharing can't have such an expectation, but perhaps the kernel needs disabling internally for synchronization at module-unload time or similar cases? If you think any of these things are problems I'll switch back to the conditional version rather than using handle_percpu_irq for everything. Rich
