Hi Leo, thanks a lot for reviewing SchedTune and pointing out this issue.
Actually going through the code I've noticed another big issue related to the definition of the acceptable regions, following commented inline. Basically, with the current implementation we was getting a correct "by chance" C region, while the acceptance for the B region was completely wrong.
In attachment a new version of the patch, please have a look and let me know if you have any doubt and/or suggestions. If the patch is ok for you, lemme also know if it's ok for you to add your sign-off.
Cheers Patrick
On 23-May 21:47, Leo Yan wrote:
On Fri, May 20, 2016 at 12:24:49AM +0800, Leo Yan wrote:
When calculate payoff criteria for performance constraint region, the inequality formula is wrong:
cap_delta / nrg_delta > cap_gain / nrg_gain
Here nrg_delta < 0, so when multiply it both side then should then multiplying nrg_delta inverts the inequality:
nrg_delta * cap_gain > cap_delta * nrg_gain
So finally we can get unified formula for both performance constraint region and performance boost region. So this patch unified these the calculation after fixed inequality formula.
Signed-off-by: Leo Yan leo.yan@linaro.org
kernel/sched/tune.c | 54 ++++++++++++++++++++++++++++------------------------- 1 file changed, 29 insertions(+), 25 deletions(-)
diff --git a/kernel/sched/tune.c b/kernel/sched/tune.c index 9d8eeb4..1da85a8 100644 --- a/kernel/sched/tune.c +++ b/kernel/sched/tune.c @@ -58,36 +58,40 @@ __schedtune_accept_deltas(int nrg_delta, int cap_delta, int perf_boost_idx, int perf_constrain_idx) { int payoff = -INT_MAX;
int idx = -1;
/* Performance Boost (B) region */
- if (nrg_delta > 0 && cap_delta > 0) {
/** Evaluate "Performance Boost" vs "Energy Increase"* payoff criteria:* cap_delta / nrg_delta < cap_gain / nrg_gain* which is:* nrg_delta * cap_gain > cap_delta * nrg_gain*/payoff = nrg_delta * threshold_gains[perf_boost_idx].cap_gain;payoff -= cap_delta * threshold_gains[perf_boost_idx].nrg_gain;return payoff;- }
- if (nrg_delta > 0 && cap_delta > 0)
Looking better at the called, I think it's worth con accept also points in the P axis, thus:
if (nrg_delta >= 0 && cap_delta > 0)
idx = perf_boost_idx;
- if (nrg_delta < 0 && cap_delta < 0) {
/** Evaluate "Performance Boost" vs "Energy Increase"* payoff criteria:* cap_delta / nrg_delta > cap_gain / nrg_gain* which is:* cap_delta * nrg_gain > nrg_delta * cap_gain*/payoff = cap_delta * threshold_gains[perf_constrain_idx].nrg_gain;payoff -= nrg_delta * threshold_gains[perf_constrain_idx].cap_gain;return payoff;- }
- else if (nrg_delta < 0 && cap_delta < 0)
For the same considerations we should better accept points in the E axis, thus:
else if (nrg_delta < 0 && cap_delta <= 0)
idx = perf_constrain_idx;/* Default: reject schedule candidate */
if (idx == -1)
return payoff;/*
* Evaluate "Performance Boost" vs "Energy Increase"** - Performance Boost (B) region** Condition: nrg_delta > 0 && cap_delta > 0* Payoff criteria:* cap_delta / nrg_delta < cap_gain / nrg_gain =
Here the inequality has a wrong direction. The schedule candidate acceptable in the B region are those for which:
cap_gain / nrg_gain < cap_delta / nrg_delta
which represents points in the "upper cut".
Thus:
* nrg_delta * cap_gain > cap_delta * nrg_gain
has to be: cap_gain * nrg_delta < cap_delta * nrg_gain
Which results into a "positive accept" payoff defined as:
payoff = (cap_delta * nrg_gain) - (cap_gain * nrg_delta)
* (note: nrg_delta > 0, nrg_gain > 0)** - Performance Constraint (C) region** Condition: nrg_delta < 0 && cap_delta < 0* payoff criteria:* cap_delta / nrg_delta > cap_gain / nrg_gain =* nrg_delta * cap_gain > cap_delta * nrg_gain
In the C region we have both a wrong definition and the sign error you reported, which turned out to provide a "by change" correct implementation, which is:
cap_gain / nrg_gain > cap_delta / nrg_delta = cap_gain * nrg_delta < cap_delta * nrg_gain
Which results into a "positive accept" payoff defined as:
payoff = (cap_delta * nrg_gain) - (cap_gain * nrg_delta)
The same as for the B region...
* (note: nrg_delta < 0, nrg_gain > 0)*/- payoff = nrg_delta * threshold_gains[perf_boost_idx].cap_gain;
- payoff -= cap_delta * threshold_gains[perf_boost_idx].nrg_gain;
Sorry, here should be:
- payoff = nrg_delta * threshold_gains[idx].cap_gain;
- payoff -= cap_delta * threshold_gains[idx].nrg_gain;
... which means that this two operations have to be inverted:
payoff = cap_delta * threshold_gains[gain_idx].nrg_gain; payoff -= nrg_delta * threshold_gains[gain_idx].cap_gain;
return payoff; }
-- 1.9.1
-- #include <best/regards.h>
Patrick Bellasi