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sched: Track the runnable average on a per-task entity basis

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Instead of tracking averaging the load parented by a cfs_rq, we can track
entity load directly. With the load for a given cfs_rq then being the sum
of its children.

To do this we represent the historical contribution to runnable average
within each trailing 1024us of execution as the coefficients of a
geometric series.

We can express this for a given task t as:

  runnable_sum(t) = \Sum u_i * y^i, runnable_avg_period(t) = \Sum 1024 * y^i
  load(t) = weight_t * runnable_sum(t) / runnable_avg_period(t)

Where: u_i is the usage in the last i`th 1024us period (approximately 1ms)
~ms and y is chosen such that y^k = 1/2.  We currently choose k to be 32 which
roughly translates to about a sched period.

Signed-off-by: Paul Turner <pjt@google.com>
Reviewed-by: Ben Segall <bsegall@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/20120823141506.372695337@google.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
This commit is contained in:
Paul Turner
2012-10-04 13:18:29 +02:00
committed by Ingo Molnar
parent 0e9e3e306c
commit 9d85f21c94
4 changed files with 151 additions and 0 deletions
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13
include/linux/sched.h
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@@ -1095,6 +1095,16 @@ struct load_weight {
unsigned long weight, inv_weight;
};
struct sched_avg {
/*
* These sums represent an infinite geometric series and so are bound
* above by 1024/(1-y). Thus we only need a u32 to store them for for all
* choices of y < 1-2^(-32)*1024.
*/
u32 runnable_avg_sum, runnable_avg_period;
u64 last_runnable_update;
};
#ifdef CONFIG_SCHEDSTATS
struct sched_statistics {
u64 wait_start;
@@ -1155,6 +1165,9 @@ struct sched_entity {
/* rq "owned" by this entity/group: */
struct cfs_rq *my_q;
#endif
#ifdef CONFIG_SMP
struct sched_avg avg;
#endif
};
struct sched_rt_entity {