On Friday, 11/17/2017 at 11:53 GMT, Sebastian Ott <[email protected]> wrote: > 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).
So what you're saying, Sebastian, is that (a) fine-grained control over what devices interrupt what CPUs is not in the Z architecture, (b) it's not in there for a good reason, (c) providing such a capability would adversely affect overall system performance (which is why it's not in the architecture in the first place). It might, however, be an interesting idea to make the ioctl()s in the device driver a no-op instead of not being present or generating its own errnos. That way folks can turn the knob, feel better, but not see any change since "it doesn't get any better than this". Alan Altmark Senior Managing z/VM and Linux Consultant IBM Systems Lab Services IBM Z Delivery Practice ibm.com/systems/services/labservices office: 607.429.3323 mobile; 607.321.7556 [email protected] IBM Endicott ---------------------------------------------------------------------- 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/
