Re: [PATCH] Skew tick for systems with a large number of processors

[kernel test robot <lkp@intel.com>]

Hi Christoph,

kernel test robot noticed the following build errors:

[auto build test ERROR on 66701750d5565c574af42bef0b789ce0203e3071]

url:    https://github.com/intel-lab-lkp/linux/commits/Christoph-Lameter-via-B4-Relay/Skew-tick-for-systems-with-a-large-number-of-processors/20250703-034357
base:   66701750d5565c574af42bef0b789ce0203e3071
patch link:    https://lore.kernel.org/r/20250702-tick_skew-v1-1-ff8d73035b02%40gentwo.org
patch subject: [PATCH] Skew tick for systems with a large number of processors
config: arc-randconfig-002-20250703 (https://download.01.org/0day-ci/archive/20250703/202507032322.5jzirIYw-lkp@intel.com/config)
compiler: arc-linux-gcc (GCC) 12.4.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20250703/202507032322.5jzirIYw-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202507032322.5jzirIYw-lkp@intel.com/

All errors (new ones prefixed by >>):

   kernel/time/tick-sched.c: In function 'tick_setup_sched_timer':
>> kernel/time/tick-sched.c:1577:44: error: 'CONFIG_TICK_SKEW_LIMIT' undeclared (first use in this function); did you mean 'CONFIG_TICK_ONESHOT'?
    1577 |                 if (num_possible_cpus() >= CONFIG_TICK_SKEW_LIMIT) {
         |                                            ^~~~~~~~~~~~~~~~~~~~~~
         |                                            CONFIG_TICK_ONESHOT
   kernel/time/tick-sched.c:1577:44: note: each undeclared identifier is reported only once for each function it appears in


vim +1577 kernel/time/tick-sched.c

  1566	
  1567	/**
  1568	 * tick_setup_sched_timer - setup the tick emulation timer
  1569	 * @hrtimer: whether to use the hrtimer or not
  1570	 */
  1571	void tick_setup_sched_timer(bool hrtimer)
  1572	{
  1573		struct tick_sched *ts = this_cpu_ptr(&tick_cpu_sched);
  1574	
  1575		/* Figure out if we should skew the tick */
  1576		if (sched_skew_tick < 0) {
> 1577			if (num_possible_cpus() >= CONFIG_TICK_SKEW_LIMIT) {
  1578				sched_skew_tick = 1;
  1579				pr_info("Tick skewed mode enabled. Possible cpus %u > %u\n",
  1580					num_possible_cpus(), CONFIG_TICK_SKEW_LIMIT);
  1581			} else
  1582				sched_skew_tick = 0;
  1583		}
  1584	
  1585		/* Emulate tick processing via per-CPU hrtimers: */
  1586		hrtimer_setup(&ts->sched_timer, tick_nohz_handler, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_HARD);
  1587	
  1588		if (IS_ENABLED(CONFIG_HIGH_RES_TIMERS) && hrtimer)
  1589			tick_sched_flag_set(ts, TS_FLAG_HIGHRES);
  1590	
  1591		/* Get the next period (per-CPU) */
  1592		hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
  1593	
  1594		/* Offset the tick to avert 'jiffies_lock' contention. */
  1595		if (sched_skew_tick) {
  1596			u64 offset = TICK_NSEC >> 1;
  1597			do_div(offset, num_possible_cpus());
  1598			offset *= smp_processor_id();
  1599			hrtimer_add_expires_ns(&ts->sched_timer, offset);
  1600		} else
  1601			pr_info("Tick operating in synchronized mode.\n");
  1602	
  1603	
  1604		hrtimer_forward_now(&ts->sched_timer, TICK_NSEC);
  1605		if (IS_ENABLED(CONFIG_HIGH_RES_TIMERS) && hrtimer)
  1606			hrtimer_start_expires(&ts->sched_timer, HRTIMER_MODE_ABS_PINNED_HARD);
  1607		else
  1608			tick_program_event(hrtimer_get_expires(&ts->sched_timer), 1);
  1609		tick_nohz_activate(ts);
  1610	}
  1611	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki