Ralf Baechle wrote: > On Thu, Aug 29, 2002 at 10:39:36AM -0700, Jun Sun wrote: > > >>Ralf Baechle wrote: > > >>> c0_compare = c0_count + mips_counter_frequency / HZ. >>> >>>That's what the individual boards are currently doing themselves though that >>>should be done in generic code. >>> >> >>Good idea. >> >>The attached patch attempts to set the first interrupt. It should be benign >>even if a system is not using CPU counter as timer interrupt. >> >>I also updated the time.README, including a new section about implementation >>on a SMP machine. > > > Applied though I think that this should also be done via start_secondary > that is we'll need some per_cpu_time_init analog to per_cpu_trap_init. Right now setting per-cpu timers is totally left to the board-dependent code. Once we see more SMP boxes using this approach, I think it starts to be interesting to make some abstraction and support it in a systematic way, including support for using CPU counter as the per-cpu timer interrupt. Using local_timer_emulation sounds like an attractive alternative to me, as we only need to set up one system-wide timer interrupt. Conceptually it probably takes a little longer to run through timer_interrupt (due to IPI calls). But if the hit on performance is very negligible, the simplicity might make it worthwile. BTW, since I am here, I like to ramble on a little bit further. Currently Linux supports two kinds of IPI (inter-processor interrupt) deliveries: 1) sender waiting for the interrupt handler to start 2) sender waiting for the interrupt handler to start and complete I think we really should the third kind: 3) sender does not wait at all. Just delivers the interrupt. With this support, the emulated local timer approach would have no performance penalty at all. Jun
