Messages in this thread Patch in this message | | | From | Chuyi Zhou <> | Subject | [PATCH] sched/core.c: Add min_ratio for cfs bandwidth_control | Date | Tue, 11 Oct 2022 20:07:21 +0800 |
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Tasks may be throttled when holding locks for a long time by current cfs bandwidth control mechanism once users set a too small quota/period ratio, which can result whole system get stuck[1].
In order to prevent the above situation from happening, this patch adds sysctl_sched_cfs_bandwidth_min_ratio in /proc/sys/kernel, which indicates the minimum percentage of quota/period users can set. The default value is zero and users can set quota and period without triggering this constraint.
Link[1]:https://lore.kernel.org/lkml/5987be34-b527-4ff5-a17d-5f6f0dc94d6d@huawei.com/T/ Signed-off-by: Chuyi Zhou <zhouchuyi@bytedance.com> Suggested-by: Abel Wu <wuyun.abel@bytedance.com> --- include/linux/sched/sysctl.h | 4 ++++ kernel/sched/core.c | 23 +++++++++++++++++++++++ kernel/sysctl.c | 10 ++++++++++ 3 files changed, 37 insertions(+)
diff --git a/include/linux/sched/sysctl.h b/include/linux/sched/sysctl.h index e650946816d0..375c14f8fca9 100644 --- a/include/linux/sched/sysctl.h +++ b/include/linux/sched/sysctl.h @@ -21,6 +21,10 @@ enum sched_tunable_scaling { SCHED_TUNABLESCALING_END, }; +#ifdef CONFIG_CFS_BANDWIDTH +extern unsigned int sysctl_sched_cfs_bandwidth_min_ratio; +#endif + #define NUMA_BALANCING_DISABLED 0x0 #define NUMA_BALANCING_NORMAL 0x1 #define NUMA_BALANCING_MEMORY_TIERING 0x2 diff --git a/kernel/sched/core.c b/kernel/sched/core.c index 60fdc0faf1c9..fc5b6671154d 100644 --- a/kernel/sched/core.c +++ b/kernel/sched/core.c @@ -10541,6 +10541,12 @@ static u64 cpu_shares_read_u64(struct cgroup_subsys_state *css, } #ifdef CONFIG_CFS_BANDWIDTH +/* + * The minimum of quota/period ratio users can set, default is zero and users can set + * quota and period without triggering this constraint. + */ +unsigned int sysctl_sched_cfs_bandwidth_min_ratio; + static DEFINE_MUTEX(cfs_constraints_mutex); const u64 max_cfs_quota_period = 1 * NSEC_PER_SEC; /* 1s */ @@ -10550,6 +10556,20 @@ static const u64 max_cfs_runtime = MAX_BW * NSEC_PER_USEC; static int __cfs_schedulable(struct task_group *tg, u64 period, u64 runtime); +static int check_cfs_bandwidth_min_ratio(u64 period, u64 quota) +{ + u64 ratio; + + if (!sysctl_sched_cfs_bandwidth_min_ratio) + return 0; + + ratio = div64_u64(quota * 100, period); + if (ratio < sysctl_sched_cfs_bandwidth_min_ratio) + return -1; + + return 0; +} + static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota, u64 burst) { @@ -10585,6 +10605,9 @@ static int tg_set_cfs_bandwidth(struct task_group *tg, u64 period, u64 quota, burst + quota > max_cfs_runtime)) return -EINVAL; + if (quota != RUNTIME_INF && check_cfs_bandwidth_min_ratio(period, quota)) + return -EINVAL; + /* * Prevent race between setting of cfs_rq->runtime_enabled and * unthrottle_offline_cfs_rqs(). diff --git a/kernel/sysctl.c b/kernel/sysctl.c index 205d605cacc5..26f05ec7d9aa 100644 --- a/kernel/sysctl.c +++ b/kernel/sysctl.c @@ -1642,6 +1642,16 @@ static struct ctl_table kern_table[] = { .extra2 = SYSCTL_FOUR, }, #endif /* CONFIG_NUMA_BALANCING */ +#ifdef CONFIG_CFS_BANDWIDTH + { + .procname = "sched_cfs_bandwidth_min_ratio", + .data = &sysctl_sched_cfs_bandwidth_min_ratio, + .maxlen = sizeof(unsigned int), + .mode = 0644, + .proc_handler = proc_dointvec_minmax, + .extra1 = SYSCTL_ZERO, + }, +#endif /* CONFIG_CFS_BANDWIDTH */ { .procname = "panic", .data = &panic_timeout, -- 2.20.1
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