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  1. 09 Sep, 2009 1 commit
    • Mike Galbraith's avatar
      sched: Turn off child_runs_first · 2bba22c5
      Mike Galbraith authored 
      Set child_runs_first default to off.

It hurts 'optimal' make -j<NR_CPUS> workloads as make jobs
get preempted by child tasks, reducing parallelism.

Note, this patch might make existing races in user
applications more prominent than before - so breakages
might be bisected to this commit.

Child-runs-first is broken on SMP to begin with, and we
already had it off briefly in v2.6.23 so most of the
offenders ought to be fixed. Would be nice not to revert
this commit but fix those apps finally ...
Signed-off-by: default avatarMike Galbraith <efault@gmx.de>
Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <1252486344.28645.18.camel@marge.simson.net>
[ made the sysctl independent of CONFIG_SCHED_DEBUG, in case
  people want to work around broken apps. ]
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
      2bba22c5
  3. 08 Sep, 2009 1 commit
    • Mike Galbraith's avatar
      sched: Ensure that a child can't gain time over it's parent after fork() · b5d9d734
      Mike Galbraith authored 
      A fork/exec load is usually "pass the baton", so the child
should never be placed behind the parent.  With START_DEBIT we
make room for the new task, but with child_runs_first, that
room comes out of the _parent's_ hide. There's nothing to say
that the parent wasn't ahead of min_vruntime at fork() time,
which means that the "baton carrier", who is essentially the
parent in drag, can gain time and increase scheduling latencies
for waiters.

With NEW_FAIR_SLEEPERS + START_DEBIT + child_runs_first
enabled, we essentially pass the sleeper fairness off to the
child, which is fine, but if we don't base placement on the
parent's updated vruntime, we can end up compounding latency
woes if the child itself then does fork/exec.  The debit
incurred at fork doesn't hurt the parent who is then going to
sleep and maybe exit, but the child who acquires the error
harms all comers.

This improves latencies of make -j<n> kernel build workloads.
Reported-by: default avatarJens Axboe <jens.axboe@oracle.com>
Signed-off-by: default avatarMike Galbraith <efault@gmx.de>
Acked-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <new-submission>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
      b5d9d734
  5. 07 Sep, 2009 3 commits
  7. 04 Sep, 2009 13 commits
  9. 02 Sep, 2009 3 commits
  11. 29 Aug, 2009 1 commit
  13. 28 Aug, 2009 2 commits
    • Peter Zijlstra's avatar
      sched: Fix division by zero - really · 34d76c41
      Peter Zijlstra authored 
      When re-computing the shares for each task group's cpu
representation we need the ratio of weight on each cpu vs the
total weight of the sched domain.

Since load-balancing is loosely (read not) synchronized, the
weight of individual cpus can change between doing the sum and
calculating the ratio.

The previous patch dealt with only one of the race scenarios,
this patch side steps them all by saving a snapshot of all the
individual cpu weights, thereby always working on a consistent
set.
Signed-off-by: default avatarPeter Zijlstra <a.p.zijlstra@chello.nl>
Cc: torvalds@linux-foundation.org
Cc: jes@sgi.com
Cc: jens.axboe@oracle.com
Cc: Balbir Singh <balbir@linux.vnet.ibm.com>
Cc: Arjan van de Ven <arjan@infradead.org>
Cc: Yinghai Lu <yinghai@kernel.org>
LKML-Reference: <1251371336.18584.77.camel@twins>
Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
      34d76c41
    • Linus Torvalds's avatar
      Linux 2.6.31-rc8 · 326ba501
      Linus Torvalds authored
      326ba501
  15. 27 Aug, 2009 16 commits
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