Commit 2bba22c5 authored by Mike Galbraith's avatar Mike Galbraith Committed by Ingo Molnar
Browse files

sched: Turn off child_runs_first 



Set child_runs_first default to off.

It hurts 'optimal' make -j<NR_CPUS> workloads as make jobs
get preempted by child tasks, reducing parallelism.

Note, this patch might make existing races in user
applications more prominent than before - so breakages
might be bisected to this commit.

Child-runs-first is broken on SMP to begin with, and we
already had it off briefly in v2.6.23 so most of the
offenders ought to be fixed. Would be nice not to revert
this commit but fix those apps finally ...

Signed-off-by: default avatarMike Galbraith <efault@gmx.de>
Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1252486344.28645.18.camel@marge.simson.net>
[ made the sysctl independent of CONFIG_SCHED_DEBUG, in case
  people want to work around broken apps. ]
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
parent b5d9d734

include/linux/sched.h

+1 −1
Original line number Diff line number Diff line
@@ -1820,8 +1820,8 @@ extern unsigned int sysctl_sched_min_granularity; 
extern unsigned int sysctl_sched_wakeup_granularity;

extern unsigned int sysctl_sched_shares_ratelimit;

extern unsigned int sysctl_sched_shares_thresh;

#ifdef CONFIG_SCHED_DEBUG

extern unsigned int sysctl_sched_child_runs_first;

#ifdef CONFIG_SCHED_DEBUG

extern unsigned int sysctl_sched_features;

extern unsigned int sysctl_sched_migration_cost;

extern unsigned int sysctl_sched_nr_migrate;

kernel/sched_fair.c

+2 −2
Original line number Diff line number Diff line
@@ -48,10 +48,10 @@ unsigned int sysctl_sched_min_granularity = 4000000ULL; 
static unsigned int sched_nr_latency = 5;



/*

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

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

 * parent will (try to) run first.

 */

const_debug unsigned int sysctl_sched_child_runs_first = 1;

unsigned int sysctl_sched_child_runs_first __read_mostly;



/*

 * sys_sched_yield() compat mode

kernel/sysctl.c

+8 −8
Original line number Diff line number Diff line
@@ -246,6 +246,14 @@ static int max_wakeup_granularity_ns = NSEC_PER_SEC; /* 1 second */ 
#endif



static struct ctl_table kern_table[] = {

	{

		.ctl_name	= CTL_UNNUMBERED,

		.procname	= "sched_child_runs_first",

		.data		= &sysctl_sched_child_runs_first,

		.maxlen		= sizeof(unsigned int),

		.mode		= 0644,

		.proc_handler	= &proc_dointvec,

	},

#ifdef CONFIG_SCHED_DEBUG

	{

		.ctl_name	= CTL_UNNUMBERED,
@@ -298,14 +306,6 @@ static struct ctl_table kern_table[] = { 
		.strategy	= &sysctl_intvec,

		.extra1		= &zero,

	},

	{

		.ctl_name	= CTL_UNNUMBERED,

		.procname	= "sched_child_runs_first",

		.data		= &sysctl_sched_child_runs_first,

		.maxlen		= sizeof(unsigned int),

		.mode		= 0644,

		.proc_handler	= &proc_dointvec,

	},

	{

		.ctl_name	= CTL_UNNUMBERED,

		.procname	= "sched_features",

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