Patch from Robert Love <rml@tech9.net>
Attached patch implements sysctl/procfs scheduler tunables, knobs which
let one play with all of the important scheduler variables:
[18:12:54]rml@phantasy:~$ ls /proc/sys/sched/
child_penalty max_sleep_avg parent_penalty
exit_weight max_timeslice prio_bonus_ratio
interactive_delta min_timeslice starvation_limit
Which may help in tuning and debugging the scheduler.
I believe Ingo did something similar to this ages ago, so original
credit for the idea goes to him.
Note the values are not checked and you can probably cause a
divide-by-zero somewhere, but only root can write these.
Patch is against 2.5.51-mm1. It also applies to 2.5.51 modulo a simple
failed hunk in sysctl.c.
Documentation/filesystems/proc.txt | 87 +++++++++++++++++++++++++++++++++++++
include/linux/sysctl.h | 16 ++++++
kernel/sched.c | 36 ++++++++++-----
kernel/sysctl.c | 48 +++++++++++++++++++-
4 files changed, 174 insertions(+), 13 deletions(-)
diff -puN Documentation/filesystems/proc.txt~scheduler-tunables Documentation/filesystems/proc.txt
--- 25/Documentation/filesystems/proc.txt~scheduler-tunables 2003-03-17 02:59:35.000000000 -0800
+++ 25-akpm/Documentation/filesystems/proc.txt 2003-03-17 02:59:35.000000000 -0800
@@ -37,6 +37,7 @@ Table of Contents
2.8 /proc/sys/net/ipv4 - IPV4 settings
2.9 Appletalk
2.10 IPX
+ 2.11 /proc/sys/sched - scheduler tunables
------------------------------------------------------------------------------
Preface
@@ -1667,6 +1668,92 @@ The /proc/net/ipx_route table holds a
gives the destination network, the router node (or Directly) and the network
address of the router (or Connected) for internal networks.
+2.11 /proc/sys/sched - scheduler tunables
+-----------------------------------------
+
+Useful knobs for tuning the scheduler live in /proc/sys/sched.
+
+child_penalty
+-------------
+
+Percentage of the parent's sleep_avg that children inherit. sleep_avg is
+a running average of the time a process spends sleeping. Tasks with high
+sleep_avg values are considered interactive and given a higher dynamic
+priority and a larger timeslice. You typically want this some value just
+under 100.
+
+exit_weight
+-----------
+
+When a CPU hog task exits, its parent's sleep_avg is reduced by a factor of
+exit_weight against the exiting task's sleep_avg.
+
+interactive_delta
+-----------------
+
+If a task is "interactive" it is reinserted into the active array after it
+has expired its timeslice, instead of being inserted into the expired array.
+How "interactive" a task must be in order to be deemed interactive is a
+function of its nice value. This interactive limit is scaled linearly by nice
+value and is offset by the interactive_delta.
+
+max_sleep_avg
+-------------
+
+max_sleep_avg is the largest value (in ms) stored for a task's running sleep
+average. The larger this value, the longer a task needs to sleep to be
+considered interactive (maximum interactive bonus is a function of
+max_sleep_avg).
+
+max_timeslice
+-------------
+
+Maximum timeslice, in milliseconds. This is the value given to tasks of the
+highest dynamic priority.
+
+min_timeslice
+-------------
+
+Minimum timeslice, in milliseconds. This is the value given to tasks of the
+lowest dynamic priority. Every task gets at least this slice of the processor
+per array switch.
+
+parent_penalty
+--------------
+
+Percentage of the parent's sleep_avg that it retains across a fork().
+sleep_avg is a running average of the time a process spends sleeping. Tasks
+with high sleep_avg values are considered interactive and given a higher
+dynamic priority and a larger timeslice. Normally, this value is 100 and thus
+task's retain their sleep_avg on fork. If you want to punish interactive
+tasks for forking, set this below 100.
+
+prio_bonus_ratio
+----------------
+
+Middle percentage of the priority range that tasks can receive as a dynamic
+priority. The default value of 25% ensures that nice values at the
+extremes are still enforced. For example, nice +19 interactive tasks will
+never be able to preempt a nice 0 CPU hog. Setting this higher will increase
+the size of the priority range the tasks can receive as a bonus. Setting
+this lower will decrease this range, making the interactivity bonus less
+apparent and user nice values more applicable.
+
+starvation_limit
+----------------
+
+Sufficiently interactive tasks are reinserted into the active array when they
+run out of timeslice. Normally, tasks are inserted into the expired array.
+Reinserting interactive tasks into the active array allows them to remain
+runnable, which is important to interactive performance. This could starve
+expired tasks, however, since the interactive task could prevent the array
+switch. To prevent starving the tasks on the expired array for too long. the
+starvation_limit is the longest (in ms) we will let the expired array starve
+at the expense of reinserting interactive tasks back into active. Higher
+values here give more preferance to running interactive tasks, at the expense
+of expired tasks. Lower values provide more fair scheduling behavior, at the
+expense of interactivity. The units are in milliseconds.
+
------------------------------------------------------------------------------
Summary
------------------------------------------------------------------------------
diff -puN include/linux/sysctl.h~scheduler-tunables include/linux/sysctl.h
--- 25/include/linux/sysctl.h~scheduler-tunables 2003-03-17 02:59:35.000000000 -0800
+++ 25-akpm/include/linux/sysctl.h 2003-03-17 02:59:35.000000000 -0800
@@ -66,7 +66,8 @@ enum
CTL_DEV=7, /* Devices */
CTL_BUS=8, /* Busses */
CTL_ABI=9, /* Binary emulation */
- CTL_CPU=10 /* CPU stuff (speed scaling, etc) */
+ CTL_CPU=10, /* CPU stuff (speed scaling, etc) */
+ CTL_SCHED=11, /* scheduler tunables */
};
/* CTL_BUS names: */
@@ -157,6 +158,19 @@ enum
VM_LOWER_ZONE_PROTECTION=20,/* Amount of protection of lower zones */
};
+/* Tunable scheduler parameters in /proc/sys/sched/ */
+enum {
+ SCHED_MIN_TIMESLICE=1, /* minimum process timeslice */
+ SCHED_MAX_TIMESLICE=2, /* maximum process timeslice */
+ SCHED_CHILD_PENALTY=3, /* penalty on fork to child */
+ SCHED_PARENT_PENALTY=4, /* penalty on fork to parent */
+ SCHED_EXIT_WEIGHT=5, /* penalty to parent of CPU hog child */
+ SCHED_PRIO_BONUS_RATIO=6, /* percent of max prio given as bonus */
+ SCHED_INTERACTIVE_DELTA=7, /* delta used to scale interactivity */
+ SCHED_MAX_SLEEP_AVG=8, /* maximum sleep avg attainable */
+ SCHED_STARVATION_LIMIT=9, /* no re-active if expired is starved */
+ SCHED_NODE_THRESHOLD=10, /* NUMA node rebalance threshold */
+};
/* CTL_NET names: */
enum
diff -puN kernel/sched.c~scheduler-tunables kernel/sched.c
--- 25/kernel/sched.c~scheduler-tunables 2003-03-17 02:59:35.000000000 -0800
+++ 25-akpm/kernel/sched.c 2003-03-17 03:01:24.000000000 -0800
@@ -62,19 +62,33 @@
*
* Minimum timeslice is 10 msecs, default timeslice is 100 msecs,
* maximum timeslice is 200 msecs. Timeslices get refilled after
- * they expire.
+ *
+ * They are configurable via /proc/sys/sched
*/
-#define MIN_TIMESLICE ( 10 * HZ / 1000)
-#define MAX_TIMESLICE (200 * HZ / 1000)
-#define CHILD_PENALTY 50
-#define PARENT_PENALTY 100
-#define EXIT_WEIGHT 3
-#define PRIO_BONUS_RATIO 25
-#define INTERACTIVE_DELTA 2
-#define MAX_SLEEP_AVG (10*HZ)
-#define STARVATION_LIMIT (10*HZ)
+
+int min_timeslice = (10 * HZ) / 1000;
+int max_timeslice = (200 * HZ) / 1000;
+int child_penalty = 50;
+int parent_penalty = 100;
+int exit_weight = 3;
+int prio_bonus_ratio = 25;
+int interactive_delta = 2;
+int max_sleep_avg = 10 * HZ;
+int starvation_limit = 10 * HZ;
+int node_threshold = 125;
+
+#define MIN_TIMESLICE (min_timeslice)
+#define MAX_TIMESLICE (max_timeslice)
+#define CHILD_PENALTY (child_penalty)
+#define PARENT_PENALTY (parent_penalty)
+#define EXIT_WEIGHT (exit_weight)
+#define PRIO_BONUS_RATIO (prio_bonus_ratio)
+#define INTERACTIVE_DELTA (interactive_delta)
+#define MAX_SLEEP_AVG (max_sleep_avg)
+#define STARVATION_LIMIT (starvation_limit)
+#define NODE_THRESHOLD (node_threshold)
+
#define TIMESLICE_GRANULARITY (HZ/20 ?: 1)
-#define NODE_THRESHOLD 125
/*
* If a task is 'interactive' then we reinsert it in the active
diff -puN kernel/sysctl.c~scheduler-tunables kernel/sysctl.c
--- 25/kernel/sysctl.c~scheduler-tunables 2003-03-17 02:59:35.000000000 -0800
+++ 25-akpm/kernel/sysctl.c 2003-03-17 02:59:35.000000000 -0800
@@ -56,6 +56,16 @@ extern char core_pattern[];
extern int cad_pid;
extern int pid_max;
extern int sysctl_lower_zone_protection;
+extern int min_timeslice;
+extern int max_timeslice;
+extern int child_penalty;
+extern int parent_penalty;
+extern int exit_weight;
+extern int prio_bonus_ratio;
+extern int interactive_delta;
+extern int max_sleep_avg;
+extern int starvation_limit;
+extern int node_threshold;
/* this is needed for the proc_dointvec_minmax for [fs_]overflow UID and GID */
static int maxolduid = 65535;
@@ -113,6 +123,7 @@ static struct ctl_table_header root_tabl
static ctl_table kern_table[];
static ctl_table vm_table[];
+static ctl_table sched_table[];
#ifdef CONFIG_NET
extern ctl_table net_table[];
#endif
@@ -157,6 +168,7 @@ static ctl_table root_table[] = {
{CTL_FS, "fs", NULL, 0, 0555, fs_table},
{CTL_DEBUG, "debug", NULL, 0, 0555, debug_table},
{CTL_DEV, "dev", NULL, 0, 0555, dev_table},
+ {CTL_SCHED, "sched", NULL, 0, 0555, sched_table},
{0}
};
@@ -377,7 +389,41 @@ static ctl_table debug_table[] = {
static ctl_table dev_table[] = {
{0}
-};
+};
+
+static ctl_table sched_table[] = {
+ {SCHED_MAX_TIMESLICE, "max_timeslice", &max_timeslice,
+ sizeof(int), 0644, NULL, &proc_dointvec_minmax,
+ &sysctl_intvec, NULL, &one, NULL},
+ {SCHED_MIN_TIMESLICE, "min_timeslice", &min_timeslice,
+ sizeof(int), 0644, NULL, &proc_dointvec_minmax,
+ &sysctl_intvec, NULL, &one, NULL},
+ {SCHED_CHILD_PENALTY, "child_penalty", &child_penalty,
+ sizeof(int), 0644, NULL, &proc_dointvec_minmax,
+ &sysctl_intvec, NULL, &zero, NULL},
+ {SCHED_PARENT_PENALTY, "parent_penalty", &parent_penalty,
+ sizeof(int), 0644, NULL, &proc_dointvec_minmax,
+ &sysctl_intvec, NULL, &zero, NULL},
+ {SCHED_EXIT_WEIGHT, "exit_weight", &exit_weight,
+ sizeof(int), 0644, NULL, &proc_dointvec_minmax,
+ &sysctl_intvec, NULL, &zero, NULL},
+ {SCHED_PRIO_BONUS_RATIO, "prio_bonus_ratio", &prio_bonus_ratio,
+ sizeof(int), 0644, NULL, &proc_dointvec_minmax,
+ &sysctl_intvec, NULL, &zero, NULL},
+ {SCHED_INTERACTIVE_DELTA, "interactive_delta", &interactive_delta,
+ sizeof(int), 0644, NULL, &proc_dointvec_minmax,
+ &sysctl_intvec, NULL, &zero, NULL},
+ {SCHED_MAX_SLEEP_AVG, "max_sleep_avg", &max_sleep_avg,
+ sizeof(int), 0644, NULL, &proc_dointvec_minmax,
+ &sysctl_intvec, NULL, &one, NULL},
+ {SCHED_STARVATION_LIMIT, "starvation_limit", &starvation_limit,
+ sizeof(int), 0644, NULL, &proc_dointvec_minmax,
+ &sysctl_intvec, NULL, &zero, NULL},
+ {SCHED_NODE_THRESHOLD, "node_threshold", &node_threshold,
+ sizeof(int), 0644, NULL, &proc_dointvec_minmax,
+ &sysctl_intvec, NULL, &one, NULL},
+ {0}
+};
extern void init_irq_proc (void);
_