From 0453b435df0d69dd0d8c42eb9b3015aaf0d8a032 Mon Sep 17 00:00:00 2001 From: Frederic Weisbecker Date: Wed, 27 Mar 2013 02:18:34 +0100 Subject: nohz: Force boot CPU outside full dynticks range The timekeeping job must be able to run early on boot because there may be some pre-SMP (and thus pre-initcalls ) components that rely on it. The IO-APIC is one such users as it tests the timer health by watching jiffies progression. Given that it happens before we know the initial online set, we can't rely on it to select a timekeeper. We need one before SMP time otherwise we simply crash on boot. To fix this and keep things simple for now, force the boot CPU outside of the full dynticks range in any case and do this early on kernel parameter parsing time. We might want a trickier solution later, expecially for aSMP architectures that need to assign housekeeping tasks to arbitrary low power CPUs. But it's still first pass KISS time for now. Reviewed-by: Paul E. McKenney Signed-off-by: Frederic Weisbecker Cc: Andrew Morton Cc: Chris Metcalf Cc: Christoph Lameter Cc: Geoff Levand Cc: Gilad Ben Yossef Cc: Hakan Akkan Cc: Ingo Molnar Cc: Kevin Hilman Cc: Li Zhong Cc: Paul E. McKenney Cc: Paul Gortmaker Cc: Peter Zijlstra Cc: Steven Rostedt Cc: Thomas Gleixner --- Documentation/kernel-parameters.txt | 4 +-- kernel/time/tick-sched.c | 54 +++++++++++-------------------------- 2 files changed, 17 insertions(+), 41 deletions(-) diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt index 82365dd..887b297 100644 --- a/Documentation/kernel-parameters.txt +++ b/Documentation/kernel-parameters.txt @@ -1916,8 +1916,8 @@ bytes respectively. Such letter suffixes can also be entirely omitted. nohz_full= [KNL,BOOT] In kernels built with CONFIG_NO_HZ_FULL=y, set the specified list of CPUs whose tick will be stopped - whenever possible. You need to keep at least one online - CPU outside the range to maintain the timekeeping. + whenever possible. The boot CPU will be forced outside + the range to maintain the timekeeping. noiotrap [SH] Disables trapped I/O port accesses. diff --git a/kernel/time/tick-sched.c b/kernel/time/tick-sched.c index 369b576..2bac5ea 100644 --- a/kernel/time/tick-sched.c +++ b/kernel/time/tick-sched.c @@ -158,11 +158,21 @@ int tick_nohz_full_cpu(int cpu) /* Parse the boot-time nohz CPU list from the kernel parameters. */ static int __init tick_nohz_full_setup(char *str) { + int cpu; + alloc_bootmem_cpumask_var(&nohz_full_mask); - if (cpulist_parse(str, nohz_full_mask) < 0) + if (cpulist_parse(str, nohz_full_mask) < 0) { pr_warning("NOHZ: Incorrect nohz_full cpumask\n"); - else - have_nohz_full_mask = true; + return 1; + } + + cpu = smp_processor_id(); + if (cpumask_test_cpu(cpu, nohz_full_mask)) { + pr_warning("NO_HZ: Clearing %d from nohz_full range for timekeeping\n", cpu); + cpumask_clear_cpu(cpu, nohz_full_mask); + } + have_nohz_full_mask = true; + return 1; } __setup("nohz_full=", tick_nohz_full_setup); @@ -195,42 +205,8 @@ static char __initdata nohz_full_buf[NR_CPUS + 1]; static int __init init_tick_nohz_full(void) { - cpumask_var_t online_nohz; - int cpu; - - if (!have_nohz_full_mask) - return 0; - - cpu_notifier(tick_nohz_cpu_down_callback, 0); - - if (!zalloc_cpumask_var(&online_nohz, GFP_KERNEL)) { - pr_warning("NO_HZ: Not enough memory to check full nohz mask\n"); - return -ENOMEM; - } - - /* - * CPUs can probably not be concurrently offlined on initcall time. - * But we are paranoid, aren't we? - */ - get_online_cpus(); - - /* Ensure we keep a CPU outside the dynticks range for timekeeping */ - cpumask_and(online_nohz, cpu_online_mask, nohz_full_mask); - if (cpumask_equal(online_nohz, cpu_online_mask)) { - pr_warning("NO_HZ: Must keep at least one online CPU " - "out of nohz_full range\n"); - /* - * We know the current CPU doesn't have its tick stopped. - * Let's use it for the timekeeping duty. - */ - preempt_disable(); - cpu = smp_processor_id(); - pr_warning("NO_HZ: Clearing %d from nohz_full range\n", cpu); - cpumask_clear_cpu(cpu, nohz_full_mask); - preempt_enable(); - } - put_online_cpus(); - free_cpumask_var(online_nohz); + if (have_nohz_full_mask) + cpu_notifier(tick_nohz_cpu_down_callback, 0); cpulist_scnprintf(nohz_full_buf, sizeof(nohz_full_buf), nohz_full_mask); pr_info("NO_HZ: Full dynticks CPUs: %s.\n", nohz_full_buf); -- cgit v1.1