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    SubjectRe: [PATCH] scheduler tunables
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    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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