2 files changed, 27 insertions, 0 deletions

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index b69cfdc12112..ea38cd1f0aba 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2532,6 +2532,15 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
 
         sched_debug     [KNL] Enables verbose scheduler debug messages.
 
+        skew_tick=      [KNL] Offset the periodic timer tick per cpu to mitigate
+                        xtime_lock contention on larger systems, and/or RCU lock
+                        contention on all systems with CONFIG_MAXSMP set.
+                        Format: { "0" | "1" }
+                        0 -- disable. (may be 1 via CONFIG_CMDLINE="skew_tick=1"
+                        1 -- enable.
+                        Note: increases power consumption, thus should only be
+                        enabled if running jitter sensitive (HPC/RT) workloads.
+
         security=       [SECURITY] Choose a security module to enable at boot.
                         If this boot parameter is not specified, only the first
                         security module asking for security registration will be
diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c
index 6a3a5b9ff561..4eddbb5ea9c5 100644
--- a/kernel/time/tick-sched.c
+++ b/kernel/time/tick-sched.c
@@ -814,6 +814,8 @@ static enum hrtimer_restart tick_sched_timer(struct hrtimer *timer)
         return HRTIMER_RESTART;
 }
 
+static int sched_skew_tick;
+
 /**
  * tick_setup_sched_timer - setup the tick emulation timer
  */
@@ -831,6 +833,14 @@ void tick_setup_sched_timer(void)
         /* Get the next period (per cpu) */
         hrtimer_set_expires(&ts->sched_timer, tick_init_jiffy_update());
 
+        /* Offset the tick to avert xtime_lock contention. */
+        if (sched_skew_tick) {
+                u64 offset = ktime_to_ns(tick_period) >> 1;
+                do_div(offset, num_possible_cpus());
+                offset *= smp_processor_id();
+                hrtimer_add_expires_ns(&ts->sched_timer, offset);
+        }
+
         for (;;) {
                 hrtimer_forward(&ts->sched_timer, now, tick_period);
                 hrtimer_start_expires(&ts->sched_timer,
@@ -910,3 +920,11 @@ int tick_check_oneshot_change(int allow_nohz)
         tick_nohz_switch_to_nohz();
         return 0;
 }
+
+static int __init skew_tick(char *str)
+{
+        get_option(&str, &sched_skew_tick);
+
+        return 0;
+}
+early_param("skew_tick", skew_tick);