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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: Mike Galbraith <efault@gmx.de> Acked-by: Peter 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: Ingo Molnar <mingo@elte.hu>
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@ -1820,8 +1820,8 @@ extern unsigned int sysctl_sched_min_granularity;
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extern unsigned int sysctl_sched_wakeup_granularity;
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extern unsigned int sysctl_sched_shares_ratelimit;
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extern unsigned int sysctl_sched_shares_thresh;
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#ifdef CONFIG_SCHED_DEBUG
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extern unsigned int sysctl_sched_child_runs_first;
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#ifdef CONFIG_SCHED_DEBUG
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extern unsigned int sysctl_sched_features;
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extern unsigned int sysctl_sched_migration_cost;
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extern unsigned int sysctl_sched_nr_migrate;
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@ -48,10 +48,10 @@ unsigned int sysctl_sched_min_granularity = 4000000ULL;
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static unsigned int sched_nr_latency = 5;
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/*
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* After fork, child runs first. (default) If set to 0 then
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* After fork, child runs first. If set to 0 (default) then
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* parent will (try to) run first.
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*/
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const_debug unsigned int sysctl_sched_child_runs_first = 1;
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unsigned int sysctl_sched_child_runs_first __read_mostly;
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/*
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* sys_sched_yield() compat mode
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@ -246,6 +246,14 @@ static int max_wakeup_granularity_ns = NSEC_PER_SEC; /* 1 second */
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#endif
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static struct ctl_table kern_table[] = {
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{
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.ctl_name = CTL_UNNUMBERED,
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.procname = "sched_child_runs_first",
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.data = &sysctl_sched_child_runs_first,
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.maxlen = sizeof(unsigned int),
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.mode = 0644,
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.proc_handler = &proc_dointvec,
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},
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#ifdef CONFIG_SCHED_DEBUG
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{
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.ctl_name = CTL_UNNUMBERED,
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@ -298,14 +306,6 @@ static struct ctl_table kern_table[] = {
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.strategy = &sysctl_intvec,
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.extra1 = &zero,
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},
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{
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.ctl_name = CTL_UNNUMBERED,
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.procname = "sched_child_runs_first",
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.data = &sysctl_sched_child_runs_first,
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.maxlen = sizeof(unsigned int),
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.mode = 0644,
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.proc_handler = &proc_dointvec,
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},
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{
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.ctl_name = CTL_UNNUMBERED,
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.procname = "sched_features",
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