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    SubjectRe: 'autogroup' sched code KILLING responsiveness
    On Sun, Jan 23, 2011 at 02:50:08AM -0800, Christian Kujau wrote:
    > On Fri, 21 Jan 2011 at 10:20, Michael Witten wrote:
    > > With that code in place, a resource-intensive activity (such as
    > > compiling the Linux kernel) causes my computer to become
    > > unresponsive for many seconds at a time; the entire screen
    > > does not refresh, typed keys are dropped or are handled very
    > > late, etc (even in Linux's plain virtual consoles).
    >
    > Unfortunately, I'd like to add a "me too". 2.6.38-rc1 behaves fine, but
    > with CONFIG_SCHED_AUTOGROUP=y and doing I/O and CPU intensive work (git
    > prune/git repack on a Linux git tree), system load goes up to ~13 and
    > becomes unresponse for some time too. This even happens when I start the
    > jobs with nice -n10.
    >
    > Without CONFIG_SCHED_AUTOGROUP enabled and doing the same work,
    > systemload goes up to 1 or maybe 2.
    >
    > I'm on UP as well (PowerPC G4), disabling CONFIG_SCHED_AUTOGROUP helps
    > here too.

    I think below patch will fix it.

    ---
    From: Yong Zhang <yong.zhang0@gmail.com>
    Subject: [PATCH] sched: tg->se->load should be initialised to tg->shares

    Michael reported that when enable autogroup on UP, system
    responsiveness becomes very bad.
    Because in init_tg_cfs_entry() we initialise se->load
    to 0 instead of tg->shares, in the end we have 0-weight
    sched entity on rq, then lead to misbehavior.

    Reported-by: Michael Witten <mfwitten@gmail.com>
    Reported-by: Christian Kujau <christian@nerdbynature.de>
    Signed-off-by: Yong Zhang <yong.zhang0@gmail.com>
    ---
    kernel/sched.c | 2 +-
    1 files changed, 1 insertions(+), 1 deletions(-)

    diff --git a/kernel/sched.c b/kernel/sched.c
    index 18d38e4..3ec2c6c 100644
    --- a/kernel/sched.c
    +++ b/kernel/sched.c
    @@ -7857,7 +7857,7 @@ static void init_tg_cfs_entry(struct task_group *tg, struct cfs_rq *cfs_rq,
    se->cfs_rq = parent->my_q;

    se->my_q = cfs_rq;
    - update_load_set(&se->load, 0);
    + update_load_set(&se->load, tg->shares);
    se->parent = parent;
    }
    #endif
    --
    1.7.1



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