On Fri, Feb 03, 2023 at 10:34:22AM +0100, Christoph Lameter wrote: > On Thu, 2 Feb 2023, Marcelo Tosatti wrote: > > > > I thought you would only run this while the kernel is not active on the > > > remote cpu? Then you dont need any cmpxchg and you can leave the function > > > as is. > > > > The remote cpu can enter kernel mode while this function executes. > > Isnt there some lock/serializtion to stall the kernel until you are done? Not that i know of. Anyway, an additional datapoint is: "Software defined PLC" (https://www.redhat.com/en/blog/software-defined-programmable-logic-controller-introduction), applications can perform system calls in their time sensitive loop. One example of an opensource software is OpenPLC. One would like to avoid interruptions for those cases as well. > > There is no mode which indicates userspace cannot enter the kernel. > > There are lot of thinngs that happen upon entry to the kernel. I would > hope that you can do something there. Scheduler? The use-case in question is with isolation, where a CPU is dedicated to a single task. So the scheduler should not be an issue.
