linux-toradex.git/kernel/sched_fair.c, branch v2.6.23.9

Fix divide-by-zero in the 2.6.23 scheduler code

2007-11-26T17:42:30+00:00

No patch in mainline as this logic has been removed from 2.6.24 so it is
not necessary.


https://bugzilla.redhat.com/show_bug.cgi?id=340161

The problem code has been removed in 2.6.24. The below patch disables
SCHED_FEAT_PRECISE_CPU_LOAD which causes the offending code to be skipped
but does not prevent the user from enabling it.

The divide-by-zero is here in kernel/sched.c:

static void update_cpu_load(struct rq *this_rq)
{
	u64 fair_delta64, exec_delta64, idle_delta64, sample_interval64, tmp64;
	unsigned long total_load = this_rq->ls.load.weight;
	unsigned long this_load =  total_load;
	struct load_stat *ls = &this_rq->ls;
	int i, scale;

	this_rq->nr_load_updates++;
	if (unlikely(!(sysctl_sched_features & SCHED_FEAT_PRECISE_CPU_LOAD)))
		goto do_avg;

	/* Update delta_fair/delta_exec fields first */
	update_curr_load(this_rq);

	fair_delta64 = ls->delta_fair + 1;
	ls->delta_fair = 0;

	exec_delta64 = ls->delta_exec + 1;
	ls->delta_exec = 0;

	sample_interval64 = this_rq->clock - ls->load_update_last;
	ls->load_update_last = this_rq->clock;

	if ((s64)sample_interval64 < (s64)TICK_NSEC)
		sample_interval64 = TICK_NSEC;

	if (exec_delta64 > sample_interval64)
		exec_delta64 = sample_interval64;

	idle_delta64 = sample_interval64 - exec_delta64;

======>	tmp64 = div64_64(SCHED_LOAD_SCALE * exec_delta64, fair_delta64);
	tmp64 = div64_64(tmp64 * exec_delta64, sample_interval64);

	this_load = (unsigned long)tmp64;

do_avg:

	/* Update our load: */
	for (i = 0, scale = 1; i < CPU_LOAD_IDX_MAX; i++, scale += scale) {
		unsigned long old_load, new_load;

		/* scale is effectively 1 << i now, and >> i divides by scale */

		old_load = this_rq->cpu_load[i];
		new_load = this_load;

		this_rq->cpu_load[i] = (old_load*(scale-1) + new_load) >> i;
	}
}

For stable only; the code has been removed in 2.6.24.

Signed-off-by: Chuck Ebbert 
Acked-by: Ingo Molnar 
Signed-off-by: Greg Kroah-Hartman

sched: fix profile=sleep

2007-10-02T12:13:08+00:00

fix sleep profiling - we lost this chunk in the CFS merge.

Found-by: Mel Gorman 
Signed-off-by: Ingo Molnar

sched: add /proc/sys/kernel/sched_compat_yield

2007-09-19T21:34:46+00:00

add /proc/sys/kernel/sched_compat_yield to make sys_sched_yield()
more agressive, by moving the yielding task to the last position
in the rbtree.

with sched_compat_yield=0:

   PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
  2539 mingo     20   0  1576  252  204 R   50  0.0   0:02.03 loop_yield
  2541 mingo     20   0  1576  244  196 R   50  0.0   0:02.05 loop

with sched_compat_yield=1:

   PID USER      PR  NI  VIRT  RES  SHR S %CPU %MEM    TIME+  COMMAND
  2584 mingo     20   0  1576  248  196 R   99  0.0   0:52.45 loop
  2582 mingo     20   0  1576  256  204 R    0  0.0   0:00.00 loop_yield

Signed-off-by: Ingo Molnar 
Signed-off-by: Peter Zijlstra

sched: fix ideal_runtime calculations for reniced tasks

2007-09-05T12:32:49+00:00

fix ideal_runtime:

  - do not scale it using niced_granularity()
    it is against sum_exec_delta, so its wall-time, not fair-time.

  - move the whole check into __check_preempt_curr_fair()
    so that wakeup preemption can also benefit from the new logic.

this also results in code size reduction:

   text    data     bss     dec     hex filename
  13391     228    1204   14823    39e7 sched.o.before
  13369     228    1204   14801    39d1 sched.o.after

Signed-off-by: Peter Zijlstra 
Signed-off-by: Ingo Molnar

sched: improve prev_sum_exec_runtime setting

2007-09-05T12:32:49+00:00

Second preparatory patch for fix-ideal runtime:

Mark prev_sum_exec_runtime at the beginning of our run, the same spot
that adds our wait period to wait_runtime. This seems a more natural
location to do this, and it also reduces the code a bit:

   text    data     bss     dec     hex filename
  13397     228    1204   14829    39ed sched.o.before
  13391     228    1204   14823    39e7 sched.o.after

Signed-off-by: Peter Zijlstra 
Signed-off-by: Ingo Molnar

sched: simplify __check_preempt_curr_fair()

2007-09-05T12:32:49+00:00

Preparatory patch for fix-ideal-runtime:

simplify __check_preempt_curr_fair(): get rid of the integer return.

   text    data     bss     dec     hex filename
  13404     228    1204   14836    39f4 sched.o.before
  13393     228    1204   14825    39e9 sched.o.after

functionality is unchanged.

Signed-off-by: Peter Zijlstra 
Signed-off-by: Ingo Molnar

sched: debug: fix cfs_rq->wait_runtime accounting

2007-09-05T12:32:49+00:00

the cfs_rq->wait_runtime debug/statistics counter was not maintained
properly - fix this.

this also removes some code:

   text    data     bss     dec     hex filename
  13420     228    1204   14852    3a04 sched.o.before
  13404     228    1204   14836    39f4 sched.o.after

Signed-off-by: Ingo Molnar 
Signed-off-by: Peter Zijlstra

sched: fix niced_granularity() shift

2007-09-05T12:32:49+00:00

fix niced_granularity(). This resulted in under-scheduling for
CPU-bound negative nice level tasks (and this in turn caused
higher than necessary latencies in nice-0 tasks).

Signed-off-by: Ingo Molnar

sched: clean up task_new_fair()

2007-08-28T10:53:24+00:00

cleanup: we have the 'se' and 'curr' entity-pointers already,
no need to use p->se and current->se.

Signed-off-by: Ingo Molnar 
Signed-off-by: Peter Zijlstra 
Signed-off-by: Mike Galbraith

sched: small schedstat fix

2007-08-28T10:53:24+00:00

small schedstat fix: the cfs_rq->wait_runtime 'sum of all runtimes'
statistics counters missed newly forked tasks and thus had a constant
negative skew. Fix this.

Signed-off-by: Ingo Molnar 
Signed-off-by: Peter Zijlstra 
Signed-off-by: Mike Galbraith