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Commit b2be5e96 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

sched: reintroduce the sched_min_granularity tunable 



we lost the sched_min_granularity tunable to a clever optimization
that uses the sched_latency/min_granularity ratio - but the ratio
is quite unintuitive to users and can also crash the kernel if the
ratio is set to 0. So reintroduce the min_granularity tunable,
while keeping the ratio maintained internally.

no functionality changed.

[ mingo@elte.hu: some fixlets. ]

Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent 2cb8600e

include/linux/sched.h

+5 −1
Original line number Diff line number Diff line
@@ -1460,12 +1460,16 @@ extern void sched_idle_next(void); 


#ifdef CONFIG_SCHED_DEBUG

extern unsigned int sysctl_sched_latency;

extern unsigned int sysctl_sched_nr_latency;

extern unsigned int sysctl_sched_min_granularity;

extern unsigned int sysctl_sched_wakeup_granularity;

extern unsigned int sysctl_sched_batch_wakeup_granularity;

extern unsigned int sysctl_sched_child_runs_first;

extern unsigned int sysctl_sched_features;

extern unsigned int sysctl_sched_migration_cost;



int sched_nr_latency_handler(struct ctl_table *table, int write,

		struct file *file, void __user *buffer, size_t *length,

		loff_t *ppos);

#endif



extern unsigned int sysctl_sched_compat_yield;

kernel/sched_debug.c

+1 −1
Original line number Diff line number Diff line
@@ -211,7 +211,7 @@ static int sched_debug_show(struct seq_file *m, void *v) 
#define PN(x) \

	SEQ_printf(m, "  .%-40s: %Ld.%06ld\n", #x, SPLIT_NS(x))

	PN(sysctl_sched_latency);

	PN(sysctl_sched_nr_latency);

	PN(sysctl_sched_min_granularity);

	PN(sysctl_sched_wakeup_granularity);

	PN(sysctl_sched_batch_wakeup_granularity);

	PN(sysctl_sched_child_runs_first);

kernel/sched_fair.c

+28 −7
Original line number Diff line number Diff line
@@ -35,16 +35,21 @@ 
const_debug unsigned int sysctl_sched_latency = 20000000ULL;



/*

 * After fork, child runs first. (default) If set to 0 then

 * parent will (try to) run first.

 * Minimal preemption granularity for CPU-bound tasks:

 * (default: 1 msec, units: nanoseconds)

 */

const_debug unsigned int sysctl_sched_child_runs_first = 1;

const_debug unsigned int sysctl_sched_min_granularity = 1000000ULL;



/*

 * Minimal preemption granularity for CPU-bound tasks:

 * (default: 2 msec, units: nanoseconds)

 * is kept at sysctl_sched_latency / sysctl_sched_min_granularity

 */

const_debug unsigned int sysctl_sched_nr_latency = 20;

const_debug unsigned int sched_nr_latency = 20;



/*

 * After fork, child runs first. (default) If set to 0 then

 * parent will (try to) run first.

 */

const_debug unsigned int sysctl_sched_child_runs_first = 1;



/*

 * sys_sched_yield() compat mode
@@ -212,6 +217,22 @@ static inline struct sched_entity *__pick_last_entity(struct cfs_rq *cfs_rq) 
 * Scheduling class statistics methods:

 */



#ifdef CONFIG_SCHED_DEBUG

int sched_nr_latency_handler(struct ctl_table *table, int write,

		struct file *filp, void __user *buffer, size_t *lenp,

		loff_t *ppos)

{

	int ret = proc_dointvec_minmax(table, write, filp, buffer, lenp, ppos);



	if (ret || !write)

		return ret;



	sched_nr_latency = DIV_ROUND_UP(sysctl_sched_latency,

					sysctl_sched_min_granularity);



	return 0;

}

#endif



/*

 * The idea is to set a period in which each task runs once.
@@ -224,7 +245,7 @@ static inline struct sched_entity *__pick_last_entity(struct cfs_rq *cfs_rq) 
static u64 __sched_period(unsigned long nr_running)

{

	u64 period = sysctl_sched_latency;

	unsigned long nr_latency = sysctl_sched_nr_latency;

	unsigned long nr_latency = sched_nr_latency;



	if (unlikely(nr_running > nr_latency)) {

		period *= nr_running;

kernel/sysctl.c

+7 −4
Original line number Diff line number Diff line
@@ -235,11 +235,14 @@ static struct ctl_table kern_table[] = { 
#ifdef CONFIG_SCHED_DEBUG

	{

		.ctl_name	= CTL_UNNUMBERED,

		.procname	= "sched_nr_latency",

		.data		= &sysctl_sched_nr_latency,

		.procname	= "sched_min_granularity_ns",

		.data		= &sysctl_sched_min_granularity,

		.maxlen		= sizeof(unsigned int),

		.mode		= 0644,

		.proc_handler	= &proc_dointvec,

		.proc_handler	= &sched_nr_latency_handler,

		.strategy	= &sysctl_intvec,

		.extra1		= &min_sched_granularity_ns,

		.extra2		= &max_sched_granularity_ns,

	},

	{

		.ctl_name	= CTL_UNNUMBERED,
@@ -247,7 +250,7 @@ static struct ctl_table kern_table[] = { 
		.data		= &sysctl_sched_latency,

		.maxlen		= sizeof(unsigned int),

		.mode		= 0644,

		.proc_handler	= &proc_dointvec_minmax,

		.proc_handler	= &sched_nr_latency_handler,

		.strategy	= &sysctl_intvec,

		.extra1		= &min_sched_granularity_ns,

		.extra2		= &max_sched_granularity_ns,