* Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > On Mon, 20 Apr 2015 20:28:32 +0200 > Ingo Molnar <mingo@xxxxxxxxxx> wrote: > > > Instrumentation - especially instrumentation that should have been > > implemented mostly in user-space, like ftrace ;-) - is another special > > case that should stay as flexible as possible via sysctls, obviously. > > I know I used ftrace as an example, but a more appropriate example > would be the sched knobs, as this is more about rcu scheduling than > anything else. > > See: > > sched_autogroup_enabled sched_rr_timeslice_ms > sched_child_runs_first sched_rt_period_us > sched_domain/ sched_rt_runtime_us > sched_latency_ns sched_shares_window_ns > sched_migration_cost_ns sched_time_avg_ms > sched_min_granularity_ns sched_tunable_scaling > sched_nr_migrate sched_wakeup_granularity_ns You are comparing apples to oranges. 1) Many of these are only sysctls if CONFIG_SCHED_DEBUG is enabled, see: triton:~/tip> git grep const_debug kernel/sched/*.c kernel/sched/core.c:const_debug unsigned int sysctl_sched_features = kernel/sched/core.c:const_debug unsigned int sysctl_sched_nr_migrate = 32; kernel/sched/core.c:const_debug unsigned int sysctl_sched_time_avg = MSEC_PER_SEC; kernel/sched/core.c:const_debug unsigned int sysctl_timer_migration = 1; kernel/sched/fair.c:const_debug unsigned int sysctl_sched_migration_cost = 500000UL; and they turn into 'const' otherwise: /* * Tunables that become constants when CONFIG_SCHED_DEBUG is off: */ #ifdef CONFIG_SCHED_DEBUG # include <linux/static_key.h> # define const_debug __read_mostly #else # define const_debug const #endif 2) A handful of them are simple on/off knobs, such as the sched_child_runs_first quirk, or the sched_autogroup_enabled. 3) There's basically just the three sched_rt_* ones that are 'true' tunables (not on/off knobs), mostly because of ABI weakness: setscheduler() has no interface for them. Note that modern scheduler policies, like SCHED_DEADLINE, get all their policy parameters from the sched_setparam() user-space ABI, they are not driven by sysctls. So my point stands. Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
