On 05.01.19 22:45, Dennis Clarke wrote: > On 1/5/19 4:21 PM, Helge Deller wrote: >> On 05.01.19 00:21, Dennis Clarke wrote: >>> On 1/4/19 6:05 PM, Helge Deller wrote: >>>> On parisc, each IRQ can only be handled by one CPU, and currently CPU0 >>>> is choosen as default for handling all IRQs by default. >>>> With this patch we now assign each requested IRQ to one of the online >>>> CPUs (and thus distribute the IRQs across all CPUs), even without an >>>> instance of irqbalance running. >>> >>> Will this take into consideration the features in default_smp_affinity >>> and allow processor cores to be considered 'non interrupt' service >>> state? >> >> It seems the feature of default_smp_affinity to disable specific cores from >> servicing interrupts doesn't work on the parisc platform. >> On a 2-CPU machine I booted with the "irqaffinity=0" kernel commandline option >> (to enable CPU#0 and disable CPU#1), which then led to a hanging kernel when >> CPU#1 ist started. >> On parisc, each CPU needs to handle at least it's timer and IPMI interrupt. >> Any idea what I should try? > > Sorry, the first question was "does this work there" and we now know it > is most likely "no". I tried similar on ppc64 and also arrived at > nothing but problems. > > I am somewhat focused on digging into RISC-V at the moment and your post > raised the question in my mind. > > One of the features I once enjoyed about Solaris was that it could > easily bring cpu cores online and offline as well as disable irq service > disruptions on any core with a trivial one line command. That's already possible on Linux (e.g. on x86,power,...). > I always wanted to port something similar over to linux but would > start with something interesting like RISC-V. There shouldn't be much to port. Even on parisc, enabling and disabling irqs on specific CPUs is possible today with simple echo-commands into the files in /proc/irq/#/... (with the exception of timer and IPI irqs). Onlining and offlining cpu cores is on my todo list for parisc. So, I think it shouldn't take much to do that on RISC-V too. > ps: Also I still have those black superdomes standing around doing > nothing and still want to get serial attached, powered up, etc. > Yet another news years resolution post-it note idea. Yes, would be interesting. Helge
