Here is a draft of a patch to do autoconfig if CONFIG_NO_HZ_FULL_ALL is set.
Subject: Simple autoconfig for tickless system This is on top of the prior patch that restricts the cpus that kthread can spawn processes on. It ensures that one processor per node is kept in regular HZ mode and also adds that cpu to the kthread_mask so that OS services (like kswapd etc) can run. On a two node system two processors will be available for kthread and OS services. The rest will be tickless and kept as free from OS services as possible. Signed-off-by: Christoph Lameter <[email protected]> Index: linux/kernel/time/tick-sched.c =================================================================== --- linux.orig/kernel/time/tick-sched.c 2013-09-05 09:10:59.000000000 -0500 +++ linux/kernel/time/tick-sched.c 2013-09-11 11:46:59.387888072 -0500 @@ -330,7 +330,30 @@ static int tick_nohz_init_all(void) } err = 0; cpumask_setall(tick_nohz_full_mask); + + /* Exempt boot processor and use it for OS services */ cpumask_clear_cpu(smp_processor_id(), tick_nohz_full_mask); + cpumask_set(smp_processor_id(), cpumask_kthread_mask); + + /* And one processor for each NUMA node */ + for_each_node(node) { + struct cpumask *m = cpumask_of_node(node); + + /* Boot node ? */ + if (node == numa_node_id()) + continue; + + /* + * Exempt the first processor on each node that has + * processors available. + */ + if (cpumask_weight(m)) { + int cpu = cpumask_first(m); + + cpumask_clear_cpu(cpu, tick_nohz_full_mask); + cpumask_set(cpu, cpu_kthread_mask); + } + } tick_nohz_full_running = true; #endif return err; Index: linux/kernel/cpu.c =================================================================== --- linux.orig/kernel/cpu.c 2013-09-11 10:45:47.686052132 -0500 +++ linux/kernel/cpu.c 2013-09-11 11:49:34.122210075 -0500 @@ -682,12 +682,14 @@ static DECLARE_BITMAP(cpu_kthread_bits, const struct cpumask *const cpu_kthread_mask = to_cpumask(cpu_kthread_bits); EXPORT_SYMBOL(cpu_kthread_mask); +#ifndef CONFIG_NO_HZ_FULL_ALL static int __init kthread_setup(char *str) { cpulist_parse(str, (struct cpumask *)&cpu_kthread_bits); return 1; } __setup("kthread=", kthread_setup); +#endif void set_cpu_possible(unsigned int cpu, bool possible) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
