On Fri, Nov 27, 2020 at 06:11:01PM +0000, Marc Zyngier wrote:
On 2020-11-27 14:15, Hanks Chen wrote:
> Support for interrupt distribution design for SMP system solutions.
As far as I know, we have been supporting interrupt distribution on
ARM SMP systems pretty well for the past... what... 15 years?
I'm sure Russell can dig out an ARM926 SMP system that even predates
that.
> With this feature enabled ,the SPI interrupts would be routed to
> all the cores rather than boot core to achieve better
> load balance of interrupt handling.
Please quantify this compared to the current distribution method.
> That is, interrupts might be serviced simultaneously on different CPUs.
They already can. What is new here? Or do you mean the *same* interrupt
being serviced by different CPUs *at the same time*? That'd be fun.
IIRC (it's been many years since I looked at the GIC), more than one CPU
is woken and if they all read the INTACK, only one of them gets the
actual IRQ number, the others see a spurious interrupt. I thought we
decided that's not an efficient way to handle interrupts, so a software
irqbalancer is better.
Has anything changed since then?
I'm also concerned that in a big.LITTLE system, you may see the big CPUs
taking the interrupts all the time, which is nice for energy efficiency.