Hi Peter, On Fri, May 09, 2014 at 03:15:20PM +0100, Peter Zijlstra wrote: > On Fri, May 09, 2014 at 02:37:27PM +0100, James Hogan wrote: > > On 11 April 2014 14:42, Peter Zijlstra <[email protected]> wrote: > > > + return !(fetch_or(&ti->flags, _TIF_NEED_RESCHED) & > > > _TIF_POLLING_NRFLAG); > > > > This breaks the build on metag, and I suspect arm64 too: > > Yep, I just got a patch for arm64.
[...] > Any SMP arch that has a polling idle function of any kind (including the > default cpu_idle_poll()). > > That said, even if that's true, not having TIF_POLLING_NRFLAG isn't > fatal, just sub-optimal in that we'll send an unconditional IPI to wake > the CPU even though its polling TIF_NEED_RESCHED and doesn't need > anything other than that write to wake up. > > Most archs have (x86) hlt or (arm) wfi like idle instructions, and if > that is your only possible idle function, you'll require the interrupt > to wake up and there's really no point to having the POLLING bit. I wonder why we still need TIF_POLLING_NRFLAG for arm64. It was on arm until commit 16a8016372c42c7628eb (sanitize tsk_is_polling()). On arm64 we use wfi for idle or a firmware call but in both cases the assumption is that we need an interrupt for waking up. So I think we should remove this macro for arm64. -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
