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    Subject[announce] CFS-devel, performance improvements

    fresh back from the Kernel Summit, Peter Zijlstra and me are pleased to
    announce the latest iteration of the CFS scheduler development tree. Our
    main focus has been on simplifications and performance - and as part of
    that we've also picked up some ideas from Roman Zippel's 'Really Fair
    Scheduler' patch as well and integrated them into CFS. We'd like to ask
    people go give these patches a good workout, especially with an eye on
    any interactivity regressions.

    The combo patch against 2.6.23-rc6 can be picked up from:

    The sched-devel.git tree can be pulled from:


    There are lots of small performance improvements in form of a
    finegrained 29-patch series. We have removed a number of features and
    metrics from CFS that might have been needed but ended up being
    superfluous - while keeping the things that worked out fine, like
    sleeper fairness. On 32-bit x86 there's a ~16% speedup (over -rc6) in
    lmbench (lat_ctx -s 0 2) results:

    (microseconds, lower is better)
    v2.6.22 2.6.23-rc6(CFS) v2.6.23-rc6-CFS-devel
    0.70 0.75 0.65
    0.62 0.66 0.63
    0.60 0.72 0.69
    0.62 0.74 0.61
    0.69 0.73 0.53
    0.66 0.73 0.63
    0.63 0.69 0.61
    0.63 0.70 0.64
    0.61 0.76 0.61
    0.69 0.74 0.63
    avg: 0.64 0.72 (+12%) 0.62 (-3%)

    there is a similar speedup on 64-bit x86 as well. We are now a bit
    faster than the O(1) scheduler was under v2.6.22 - even on 32-bit. The
    main speedup comes from the avoidance of divisions (or shifts) in the
    wakeup and context-switch fastpaths.

    there's also a visible reduction in code size:

    text data bss dec hex filename
    13369 228 2036 15633 3d11 sched.o.before (UP, nodebug)
    11167 224 1988 13379 3443 sched.o.after (UP, nodebug)

    which obviously helps embedded and is good for performance as well. Even
    on 32-bit we are now within 1% of the size of v2.6.22's sched.o, which

    text data bss dec hex filename
    9915 24 3344 13283 33e3 sched.o.v2.6.22

    and on SMP the new scheduler is now substantially smaller:

    text data bss dec hex filename
    24972 4149 24 29145 71d9 sched.o-v2.6.22
    24056 2594 16 26666 682a sched.o-CFS-devel

    Changes: besides the many micro-optimizations, one of the changes is
    that se->vruntime (virtual runtime) based scheduling has been introduced
    gradually, step by step - while keeping the wait_runtime metric working
    too. (so that the two methods are comparable side by side, in the same

    The ->vruntime metric is similar to the ->time_norm metric used by
    Roman's patch (and both are losely related to the already existing
    sum_exec_runtime metric in CFS), it's in essence the sum of CPU time
    executed by a task, in nanoseconds - weighted up or down by their nice
    level (or kept the same on the default nice 0 level). Besides this basic
    metric our implementation and math differs from RFS. The two approaches
    should be conceptually more comparable from now on.

    We have also picked up two cleanups from RFS (the cfs_rq->curr approach
    and an uninlining optimization) and there's also a cleanup patch from
    Matthias Kaehlcke. We welcome and encourage finegrained patches against
    this patchset. As usual, bugreports, fixes and suggestions are welcome,

    Ingo, Peter

    Matthias Kaehlcke (1):
    sched: use list_for_each_entry_safe() in __wake_up_common()

    Peter Zijlstra (5):
    sched: simplify SCHED_FEAT_* code
    sched: new task placement for vruntime
    sched: simplify adaptive latency
    sched: clean up new task placement
    sched: add tree based averages

    Ingo Molnar (23):
    sched: fix new-task method
    sched: small sched_debug cleanup
    sched: debug: track maximum 'slice'
    sched: uniform tunings
    sched: use constants if !CONFIG_SCHED_DEBUG
    sched: remove stat_gran
    sched: remove precise CPU load
    sched: remove precise CPU load calculations #2
    sched: track cfs_rq->curr on !group-scheduling too
    sched: cleanup: simplify cfs_rq_curr() methods
    sched: uninline __enqueue_entity()/__dequeue_entity()
    sched: speed up update_load_add/_sub()
    sched: clean up calc_weighted()
    sched: introduce se->vruntime
    sched: move sched_feat() definitions
    sched: optimize vruntime based scheduling
    sched: simplify check_preempt() methods
    sched: wakeup granularity fix
    sched: add se->vruntime debugging
    sched: debug: update exec_clock only when SCHED_DEBUG
    sched: remove wait_runtime limit
    sched: remove wait_runtime fields and features
    sched: x86: allow single-depth wchan output

    arch/i386/Kconfig | 11
    include/linux/sched.h | 17 -
    kernel/sched.c | 196 ++++-------------
    kernel/sched_debug.c | 86 +++----
    kernel/sched_fair.c | 557 +++++++++++++-------------------------------------
    kernel/sysctl.c | 22 -
    6 files changed, 243 insertions(+), 646 deletions(-)
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      Last update: 2007-09-11 22:17    [W:0.027 / U:33.580 seconds]
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