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.
Thanks. > > 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. Reentrancy is possible of course if the kernel enables irqs during the irq handler. Is not doing so a stable part of the kernel irq subsystem? My understanding is that modern kernels keep irqs disabled for the full duration of (hard) irq handlers. > Once you make > the hardware capable of delivering them on either core the picture changes. *nod* Perhaps if/when we do that, the path of least resistence would be to adjust the irq numbering so that percpu (i.e., hard-routed to a particular cpu) and global irqs (deliverable on any core) are in different ranges and the existing kernel frameworks work. Rich
