On Fri, 17 Nov 2017, Timothy Sipples wrote: > Sebastian Ott wrote: > >Setting irq affinity is currently not supported on s390. > > This platform's I/O architecture is unique. What are the real-world issues > associated with not being able to set this parameter on this platform? And > what are the suggested mitigations?
It's a performance tuning knob - a mechanism for device drivers (and administrators) to specifiy that they expect an interrupt on the CPU that they used for IO submission. Since all interrupts are floating on s390, we rely on the channel subsystem to pick a good CPU to deliver the interrupt to. And most of the time the channel subsystem is good at this - also it has information a device driver has not (e.g. is a CPU in use by another guest). Also it's worth noting that we use interrupt avoidance mechanisms in our PCI implementation and for low-latency workloads device drivers poll for IO completion. There might be workloads that could benefit from IRQ affinity support but I'm not aware of this having a significant performance impact on current hardware. Sebastian ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to [email protected] with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390 ---------------------------------------------------------------------- For more information on Linux on System z, visit http://wiki.linuxvm.org/
