On 2016年05月26日 17:44, eas-dev-request(a)lists.linaro.org wrote:
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> Today's Topics:
>
> 1. Re: [PATCH] sched/tune: fix payoff calculation for
> performance constraint region (Patrick Bellasi)
> 2. Re: [PATCH] sched/tune: fix payoff calculation for
> performance constraint region (Leo Yan)
> 3. Re: [PATCH] sched/tune: fix payoff calculation for
> performance constraint region (Patrick Bellasi)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Wed, 25 May 2016 18:53:28 +0100
> From: Patrick Bellasi <patrick.bellasi(a)arm.com>
> To: Leo Yan <leo.yan(a)linaro.org>
> Cc: eas-dev(a)lists.linaro.org
> Subject: Re: [Eas-dev] [PATCH] sched/tune: fix payoff calculation for
> performance constraint region
> Message-ID: <20160525175328.GA15730@e105326-lin>
> Content-Type: text/plain; charset="utf-8"
>
> 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(a)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;
>>> /* Performance Constraint (C) 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:
>>> - * 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 =
>
Looking better to put the condition "nrg_delta == 0" or "cap_delta == 0"
in function "accept_deltas", to avoid fetch rcu lock and more functions
called, thus:
/* Optimal (O) region */
if ((nrg_delta < 0 && cap_delta >= 0) || (nrg_delta <=0 && cap_delta >
0)) {
trace_sched_tune_filter(nrg_delta, cap_delta, 0, 0, 1, 0);
return INT_MAX;
}
> 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
>>>
>>
>
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