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SubjectRe: [PATCH] scheduler tunables
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Date
On Tue, 2002-12-10 at 18:27, Robert Love wrote:

> Attached patch implements sysctl/procfs scheduler tunables, knobs
> which let one play with all of the important scheduler variables:

Updated version at Andrew's prodding, now with documentation in
Documentation/filesystem/proc.txt

Again, this patch implements scheduler tunables in /proc/sys/sched:

sched.starvation_limit = 2000
sched.max_sleep_avg = 2000
sched.interactive_delta = 2
sched.prio_bonus_ratio = 25
sched.exit_weight = 3
sched.parent_penalty = 100
sched.child_penalty = 95
sched.min_timeslice = 10
sched.max_timeslice = 300

Some notes for testers and tuners:

- you can effectively disable the interactivity estimator (both
bonuses and penalties) by setting prio_bonus_ratio to zero

- some users seem to prefer a lower child_penalty (50 is the
default in 2.4-aa)

- some workloads may benefit from setting starvation_limit lower
(maybe 0.5s?) while a few workloads may actually like it
much higher (4s?)

Enjoy,

Robert Love


Documentation/filesystems/proc.txt | 87 +++++++++++++++++++++++++++++++++++++
include/linux/sysctl.h | 15 +++++-
kernel/sched.c | 31 +++++++++----
kernel/sysctl.c | 35 ++++++++++++++
4 files changed, 157 insertions(+), 11 deletions(-)

diff -urN linux-2.5.51-mm1/Documentation/filesystems/proc.txt linux/Documentation/filesystems/proc.txt
--- linux-2.5.51-mm1/Documentation/filesystems/proc.txt 2002-12-10 17:48:09.000000000 -0500
+++ linux/Documentation/filesystems/proc.txt 2002-12-10 23:15:19.000000000 -0500
@@ -37,6 +37,7 @@
2.8 /proc/sys/net/ipv4 - IPV4 settings
2.9 Appletalk
2.10 IPX
+ 2.11 /proc/sys/sched - scheduler tunables

------------------------------------------------------------------------------
Preface
@@ -1663,6 +1664,92 @@
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 -urN linux-2.5.51-mm1/include/linux/sysctl.h linux/include/linux/sysctl.h
--- linux-2.5.51-mm1/include/linux/sysctl.h 2002-12-10 17:48:10.000000000 -0500
+++ linux/include/linux/sysctl.h 2002-12-10 16:50:41.000000000 -0500
@@ -66,7 +66,8 @@
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 +158,18 @@
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 */
+};

/* CTL_NET names: */
enum
diff -urN linux-2.5.51-mm1/kernel/sched.c linux/kernel/sched.c
--- linux-2.5.51-mm1/kernel/sched.c 2002-12-10 17:48:10.000000000 -0500
+++ linux/kernel/sched.c 2002-12-10 16:33:34.000000000 -0500
@@ -57,16 +57,29 @@
* Minimum timeslice is 10 msecs, default timeslice is 150 msecs,
* maximum timeslice is 300 msecs. Timeslices get refilled after
* they expire.
+ *
+ * They are configurable via /proc/sys/sched
*/
-#define MIN_TIMESLICE ( 10 * HZ / 1000)
-#define MAX_TIMESLICE (300 * HZ / 1000)
-#define CHILD_PENALTY 95
-#define PARENT_PENALTY 100
-#define EXIT_WEIGHT 3
-#define PRIO_BONUS_RATIO 25
-#define INTERACTIVE_DELTA 2
-#define MAX_SLEEP_AVG (2*HZ)
-#define STARVATION_LIMIT (2*HZ)
+
+int min_timeslice = (10 * HZ) / 1000;
+int max_timeslice = (300 * HZ) / 1000;
+int child_penalty = 95;
+int parent_penalty = 100;
+int exit_weight = 3;
+int prio_bonus_ratio = 25;
+int interactive_delta = 2;
+int max_sleep_avg = 2 * HZ;
+int starvation_limit = 2 * HZ;
+
+#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)

/*
* If a task is 'interactive' then we reinsert it in the active
diff -urN linux-2.5.51-mm1/kernel/sysctl.c linux/kernel/sysctl.c
--- linux-2.5.51-mm1/kernel/sysctl.c 2002-12-10 17:48:10.000000000 -0500
+++ linux/kernel/sysctl.c 2002-12-10 17:05:04.000000000 -0500
@@ -54,6 +54,15 @@
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;

/* this is needed for the proc_dointvec_minmax for [fs_]overflow UID and GID */
static int maxolduid = 65535;
@@ -111,6 +120,7 @@

static ctl_table kern_table[];
static ctl_table vm_table[];
+static ctl_table sched_table[];
#ifdef CONFIG_NET
extern ctl_table net_table[];
#endif
@@ -155,6 +165,7 @@
{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}
};

@@ -357,7 +368,29 @@

static ctl_table dev_table[] = {
{0}
-};
+};
+
+static ctl_table sched_table[] = {
+ {SCHED_MAX_TIMESLICE, "max_timeslice",
+ &max_timeslice, sizeof(int), 0644, NULL, &proc_dointvec},
+ {SCHED_MIN_TIMESLICE, "min_timeslice",
+ &min_timeslice, sizeof(int), 0644, NULL, &proc_dointvec},
+ {SCHED_CHILD_PENALTY, "child_penalty",
+ &child_penalty, sizeof(int), 0644, NULL, &proc_dointvec},
+ {SCHED_PARENT_PENALTY, "parent_penalty",
+ &parent_penalty, sizeof(int), 0644, NULL, &proc_dointvec},
+ {SCHED_EXIT_WEIGHT, "exit_weight",
+ &exit_weight, sizeof(int), 0644, NULL, &proc_dointvec},
+ {SCHED_PRIO_BONUS_RATIO, "prio_bonus_ratio",
+ &prio_bonus_ratio, sizeof(int), 0644, NULL, &proc_dointvec},
+ {SCHED_INTERACTIVE_DELTA, "interactive_delta",
+ &interactive_delta, sizeof(int), 0644, NULL, &proc_dointvec},
+ {SCHED_MAX_SLEEP_AVG, "max_sleep_avg",
+ &max_sleep_avg, sizeof(int), 0644, NULL, &proc_dointvec},
+ {SCHED_STARVATION_LIMIT, "starvation_limit",
+ &starvation_limit, sizeof(int), 0644, NULL, &proc_dointvec},
+ {0}
+};

extern void init_irq_proc (void);




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