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    SubjectRe: sysbench+mysql(oltp, readonly) 30% regression with 2.6.26-rc1
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    Date
    On Wed, 2008-05-07 at 12:55 +0800, Zhang, Yanmin wrote:
    > Comparing with kernel 2.6.25, sysbench+mysql(oltp, readonly) has many
    > regression with 2.6.26-rc1.
    >
    > 1) 8-core stoakley: 28%;
    > 2) 16-core tigerton: 20%;
    > 3) Itanium Montvale: 50%.
    >
    > Bisect located below patch.
    >
    > 8f1bc385cfbab474db6c27b5af1e439614f3025c is first bad commit
    > commit 8f1bc385cfbab474db6c27b5af1e439614f3025c
    > Author: Peter Zijlstra <a.p.zijlstra@chello.nl>
    > Date: Sat Apr 19 19:45:00 2008 +0200
    >
    > sched: fair: weight calculations
    >
    > In order to level the hierarchy, we need to calculate load based on the
    > root view. That is, each task's load is in the same unit.
    >
    >
    >
    > After I manually reverted the patch against 2.6.26-rc1 while fixing a couple of
    > conflictions/errors, sysbench oltp regression became less than 3% on 8-core
    > stoakley.

    Does this patch help?

    ---
    From: Mike Galbraith <efault@gmx.de>
    Subject: sched: fix weight calculations

    The conversion between virtual and real time is as follows:

    dvt = rw/w * dt <=> dt = w/rw * dvt

    Since we want the fair sleeper granularity to be in real time, we actually
    need to do:

    dvt = - rw/w * l

    Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
    ---
    kernel/sched_fair.c | 11 ++++++++---
    1 file changed, 8 insertions(+), 3 deletions(-)

    Index: linux-2.6-2/kernel/sched_fair.c
    ===================================================================
    --- linux-2.6-2.orig/kernel/sched_fair.c
    +++ linux-2.6-2/kernel/sched_fair.c
    @@ -662,10 +662,15 @@ place_entity(struct cfs_rq *cfs_rq, stru
    if (!initial) {
    /* sleeps upto a single latency don't count. */
    if (sched_feat(NEW_FAIR_SLEEPERS)) {
    + unsigned long thresh = sysctl_sched_latency;
    +
    + /*
    + * convert the sleeper threshold into virtual time
    + */
    if (sched_feat(NORMALIZED_SLEEPER))
    - vruntime -= calc_delta_weight(sysctl_sched_latency, se);
    - else
    - vruntime -= sysctl_sched_latency;
    + thresh = calc_delta_fair(thresh, se);
    +
    + vruntime -= thresh;
    }

    /* ensure we never gain time by being placed backwards. */

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