Hi Peter,

[FYI, it's a private test report for your RFC patch.]
[auto build test WARNING on tip/sched/core]
[also build test WARNING on next-20200528]
[cannot apply to tip/auto-latest linus/master linux/master v5.7-rc7]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url:    https://github.com/0day-ci/linux/commits/Peter-Zijlstra/Fix-the-scheduler-IPI-mess/20200527-010828
base:   https://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git 2ebb17717550607bcd85fb8cf7d24ac870e9d762
config: arm64-allyesconfig (attached as .config)
compiler: aarch64-linux-gcc (GCC) 9.3.0
reproduce (this is a W=1 build):
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        COMPILER_INSTALL_PATH=$HOME/0day COMPILER=gcc-9.3.0 make.cross ARCH=arm64 

If you fix the issue, kindly add following tag as appropriate
Reported-by: kbuild test robot <lkp@intel.com>

All warnings (new ones prefixed by >>, old ones prefixed by <<):

kernel//sched/core.c:2116:6: warning: no previous prototype for 'sched_set_stop_task' [-Wmissing-prototypes]
2116 | void sched_set_stop_task(int cpu, struct task_struct *stop)
|      ^~~~~~~~~~~~~~~~~~~
>> kernel//sched/core.c:2299:6: warning: no previous prototype for 'send_call_function_single_ipi' [-Wmissing-prototypes]
2299 | void send_call_function_single_ipi(int cpu)
|      ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

vim +/send_call_function_single_ipi +2299 kernel//sched/core.c

  2298	
> 2299	void send_call_function_single_ipi(int cpu)
  2300	{
  2301		struct rq *rq = cpu_rq(cpu);
  2302	
  2303		if (!set_nr_if_polling(rq->idle))
  2304			arch_send_call_function_single_ipi(cpu);
  2305		else
  2306			trace_sched_wake_idle_without_ipi(cpu);
  2307	}
  2308	

---
0-DAY CI Kernel Test Service, Intel Corporation
https://lists.01.org/hyperkitty/list/kbuild-all(a)lists.01.org