On 02/26/2015 02:02 PM, Paolo Bonzini wrote: > > > On 24/02/2015 00:27, Scott Wood wrote: >> This isn't a host PIC driver. It's guest PIC emulation, some of which >> is indeed not suitable for a rawlock (in particular, openpic_update_irq >> which loops on the number of vcpus, with a loop body that calls >> IRQ_check() which loops over all pending IRQs). > > The question is what behavior is wanted of code that isn't quite > RT-ready. What is preferred, bugs or bad latency? > > If the answer is bad latency (which can be avoided simply by not running > KVM on a RT kernel in production), patch 1 can be applied. If the can be applied *but* makes no difference if applied or not.
> answer is bugs, patch 1 is not upstream material. > > I myself prefer to have bad latency; if something takes a spinlock in > atomic context, that spinlock should be raw. If it hurts (latency), > don't do it (use the affected code). The problem, that is fixed by this s/spin_lock/raw_spin_lock/, exists only in -RT. There is no change upstream. In general we fix such things in -RT first and forward the patches upstream if possible. This convert thingy would be possible. Bug fixing comes before latency no matter if RT or not. Converting every lock into a rawlock is not always the answer. Last thing I read from Scott is that he is not entirely sure if this is the right approach or not and patch #1 was not acked-by him either. So for now I wait for Scott's feedback and maybe a backtrace :) > > Paolo Sebastian _______________________________________________ Linuxppc-dev mailing list Linuxppc-dev@lists.ozlabs.org https://lists.ozlabs.org/listinfo/linuxppc-dev
