Thomas De Schampheleire wrote:
> Hi,
>
> In uts/sun4u/os/mach_startup.c, there is a function
> mach_cpu_halt_idle() which is called from startup_end() in
> uts/sun4u/os/startup.c
>
> This function has the following contents:
>
> 385 void
> 386 mach_cpu_halt_idle()
> 387 {
> 388 if (enable_halt_idle_cpus) {
> 389 if (&cpu_halt_cpu) {
> 390 idle_cpu = cpu_halt;
> 391 disp_enq_thread = cpu_wakeup;
> 392 }
> 393 }
> 394 }
>
> The cpu_halt_cpu() function is only defined for some platforms, in
> sun4u the only one I find is "olympus".
>
> In my research project we are using a full system simulator in which
> OpenSolaris runs. I would like to make OpenSolaris believe that
> halting is possible by providing my own cpu_halt_cpu() function.
>
> If I provide such a function in a kernel module, can I then re-call
> mach_cpu_halt_idle() in order to overwrite the idle_cpu() and
> disp_enq_thread() pointers? Or will this result in panic or incorrect
> behavior?
>
No. mach_cpu_halt_idle() should only be called in system startup
before scheduling starts. mach_cpu_halt_idle() was not intended to
change the idle_cpu and disp_enq_thread function pointers on the fly.
*You could modify cpu_halt() and cpu_wakeup() and your new
functions to handle changing on a live system.
> If this is not possible from a module, I would like to statically add
> this cpu_halt_cpu() to the correct file in uts/sun4u/cpu/ so it is
> seen at startup. I don't know which one this would be however. I am
> simulating a serengeti machine, but there are no serengeti-specific
> files in this directory. Shall I then simply put the code in the
> us3_common files?
Later Serengeti systems have cheetah processors. Either
uts/sun4u/cpu/us3_common* or uts/sun4u/cpu/us3_cheetah* files
should work.
>
> Just to be sure: this halt_cpu mechanism will overwrite the idle loop
> so as to halt upon idling, and wakeup when some task has to run,
> right? This halting can enable energy savings.
Yes. I assume your new implementation will use poke_cpu() to
wake up the idle cpus with an Inter Processor Interrupt?
Regards,
Bill Holler
> Thanks, Thomas
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