The increased load resolution (fixed point arithmetic range) is unconditionally deactivated with #if 0, so it is effectively broken.
But the increased load range is still used somewhere (e.g., in Google), so we keep this feature. The reconciliation is we define CONFIG_CFS_INCREASE_LOAD_RANGE and it depends on FAIR_GROUP_SCHED and 64BIT and BROKEN. Suggested-by: Ingo Molnar <[email protected]> Signed-off-by: Yuyang Du <[email protected]> --- init/Kconfig | 16 +++++++++++++++ kernel/sched/sched.h | 55 +++++++++++++++++++++------------------------------- 2 files changed, 38 insertions(+), 33 deletions(-) diff --git a/init/Kconfig b/init/Kconfig index 2232080..d072c09 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -1025,6 +1025,22 @@ config CFS_BANDWIDTH restriction. See tip/Documentation/scheduler/sched-bwc.txt for more information. +config CFS_INCREASE_LOAD_RANGE + bool "Increase kernel load range" + depends on 64BIT && BROKEN + default n + help + Increase resolution of nice-level calculations for 64-bit architectures. + The extra resolution improves shares distribution and load balancing of + low-weight task groups (eg. nice +19 on an autogroup), deeper taskgroup + hierarchies, especially on larger systems. This is not a user-visible change + and does not change the user-interface for setting shares/weights. + We increase resolution only if we have enough bits to allow this increased + resolution (i.e. BITS_PER_LONG > 32). The costs for increasing resolution + when BITS_PER_LONG <= 32 are pretty high and the returns do not justify the + increased costs. + Currently broken: it increases power usage under light load. + config RT_GROUP_SCHED bool "Group scheduling for SCHED_RR/FIFO" depends on CGROUP_SCHED diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h index ebe16e3..1bb0d69 100644 --- a/kernel/sched/sched.h +++ b/kernel/sched/sched.h @@ -42,39 +42,6 @@ static inline void update_cpu_load_active(struct rq *this_rq) { } #define NS_TO_JIFFIES(TIME) ((unsigned long)(TIME) / (NSEC_PER_SEC / HZ)) /* - * Increase resolution of nice-level calculations for 64-bit architectures. - * The extra resolution improves shares distribution and load balancing of - * low-weight task groups (eg. nice +19 on an autogroup), deeper taskgroup - * hierarchies, especially on larger systems. This is not a user-visible change - * and does not change the user-interface for setting shares/weights. - * - * We increase resolution only if we have enough bits to allow this increased - * resolution (i.e. BITS_PER_LONG > 32). The costs for increasing resolution - * when BITS_PER_LONG <= 32 are pretty high and the returns do not justify the - * increased costs. - */ -#if 0 /* BITS_PER_LONG > 32 -- currently broken: it increases power usage under light load */ -# define NICE_0_LOAD_SHIFT (SCHED_FIXEDPOINT_SHIFT + SCHED_FIXEDPOINT_SHIFT) -# define user_to_kernel_load(w) ((w) << SCHED_FIXEDPOINT_SHIFT) -# define kernel_to_user_load(w) ((w) >> SCHED_FIXEDPOINT_SHIFT) -#else -# define NICE_0_LOAD_SHIFT (SCHED_FIXEDPOINT_SHIFT) -# define user_to_kernel_load(w) (w) -# define kernel_to_user_load(w) (w) -#endif - -/* - * Task weight (visible to user) and its load (invisible to user) have - * independent resolution, but they should be well calibrated. We use - * user_to_kernel_load() and kernel_to_user_load(w) to convert between - * them. The following must be true: - * - * user_to_kernel_load(sched_prio_to_weight[USER_PRIO(NICE_TO_PRIO(0))]) == NICE_0_LOAD - * kernel_to_user_load(NICE_0_LOAD) == sched_prio_to_weight[USER_PRIO(NICE_TO_PRIO(0))] - */ -#define NICE_0_LOAD (1L << NICE_0_LOAD_SHIFT) - -/* * Single value that decides SCHED_DEADLINE internal math precision. * 10 -> just above 1us * 9 -> just above 0.5us @@ -1150,6 +1117,28 @@ extern const int sched_prio_to_weight[40]; extern const u32 sched_prio_to_wmult[40]; /* + * Task weight (visible to user) and its load (invisible to user) have + * independent ranges, but they should be well calibrated. We use + * user_to_kernel_load() and kernel_to_user_load(w) to convert between + * them. + * + * The following must also be true: + * user_to_kernel_load(sched_prio_to_weight[USER_PRIO(NICE_TO_PRIO(0))]) == NICE_0_LOAD + * kernel_to_user_load(NICE_0_LOAD) == sched_prio_to_weight[USER_PRIO(NICE_TO_PRIO(0))] + */ +#ifdef CONFIG_CFS_INCREASE_LOAD_RANGE +#define NICE_0_LOAD_SHIFT (SCHED_FIXEDPOINT_SHIFT + SCHED_FIXEDPOINT_SHIFT) +#define user_to_kernel_load(w) (w << SCHED_FIXEDPOINT_SHIFT) +#define kernel_to_user_load(w) (w >> SCHED_FIXEDPOINT_SHIFT) +#else +#define NICE_0_LOAD_SHIFT (SCHED_FIXEDPOINT_SHIFT) +#define user_to_kernel_load(w) (w) +#define kernel_to_user_load(w) (w) +#endif + +#define NICE_0_LOAD (1UL << NICE_0_LOAD_SHIFT) + +/* * {de,en}queue flags: * * DEQUEUE_SLEEP - task is no longer runnable -- 2.1.4
