Messages in this thread | | | Subject | Re: [PATCH v2] cpufreq: conservative: Decrease frequency faster when the update deferred | From | Stratos Karafotis <> | Date | Tue, 15 Nov 2016 00:53:19 +0200 |
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On 15/11/2016 12:09 πμ, Rafael J. Wysocki wrote: > On Mon, Nov 14, 2016 at 10:59 PM, Rafael J. Wysocki <rafael@kernel.org> wrote: >> On Mon, Nov 14, 2016 at 10:46 PM, Stratos Karafotis >> <stratosk@semaphore.gr> wrote: >>> >>> >>> On 14/11/2016 10:44 μμ, Rafael J. Wysocki wrote: >>>> On Sat, Nov 12, 2016 at 10:04 PM, Stratos Karafotis >>>> <stratosk@semaphore.gr> wrote: >>>>> Conservative governor changes the CPU frequency in steps. >>>>> That means that if a CPU runs at max frequency, it will need several >>>>> sampling periods to return to min frequency when the workload >>>>> is finished. >>>>> >>>>> If the update function that calculates the load and target frequency >>>>> is deferred, the governor might need even more time to decrease the >>>>> frequency. >>>>> >>>>> This may have impact to power consumption and after all conservative >>>>> should decrease the frequency if there is no workload at every sampling >>>>> rate. >>>>> >>>>> To resolve the above issue calculate the number of sampling periods >>>>> that the update is deferred. Considering that for each sampling period >>>>> conservative should drop the frequency by a freq_step because the >>>>> CPU was idle apply the proper subtraction to requested frequency. >>>>> >>>>> Below, the kernel trace with and without this patch. First an >>>>> intensive workload is applied on a specific CPU. Then the workload >>>>> is removed and the CPU goes to idle. >>>>> >>>>> WITHOUT >>>>> >>>>> <idle>-0 [007] dN.. 620.329153: cpu_idle: state=4294967295 cpu_id=7 >>>>> kworker/7:2-556 [007] .... 620.350857: cpu_frequency: state=1700000 cpu_id=7 >>>>> kworker/7:2-556 [007] .... 620.370856: cpu_frequency: state=1900000 cpu_id=7 >>>>> kworker/7:2-556 [007] .... 620.390854: cpu_frequency: state=2100000 cpu_id=7 >>>>> kworker/7:2-556 [007] .... 620.411853: cpu_frequency: state=2200000 cpu_id=7 >>>>> kworker/7:2-556 [007] .... 620.432854: cpu_frequency: state=2400000 cpu_id=7 >>>>> kworker/7:2-556 [007] .... 620.453854: cpu_frequency: state=2600000 cpu_id=7 >>>>> kworker/7:2-556 [007] .... 620.494856: cpu_frequency: state=2900000 cpu_id=7 >>>>> kworker/7:2-556 [007] .... 620.515856: cpu_frequency: state=3100000 cpu_id=7 >>>>> kworker/7:2-556 [007] .... 620.536858: cpu_frequency: state=3300000 cpu_id=7 >>>>> kworker/7:2-556 [007] .... 620.557857: cpu_frequency: state=3401000 cpu_id=7 >>>>> <idle>-0 [007] d... 669.591363: cpu_idle: state=4 cpu_id=7 >>>>> <idle>-0 [007] d... 669.591939: cpu_idle: state=4294967295 cpu_id=7 >>>>> <idle>-0 [007] d... 669.591980: cpu_idle: state=4 cpu_id=7 >>>>> <idle>-0 [007] dN.. 669.591989: cpu_idle: state=4294967295 cpu_id=7 >>>>> ... >>>>> <idle>-0 [007] d... 670.201224: cpu_idle: state=4 cpu_id=7 >>>>> <idle>-0 [007] d... 670.221975: cpu_idle: state=4294967295 cpu_id=7 >>>>> kworker/7:2-556 [007] .... 670.222016: cpu_frequency: state=3300000 cpu_id=7 >>>>> <idle>-0 [007] d... 670.222026: cpu_idle: state=4 cpu_id=7 >>>>> <idle>-0 [007] d... 670.234964: cpu_idle: state=4294967295 cpu_id=7 >>>>> ... >>>>> <idle>-0 [007] d... 670.801251: cpu_idle: state=4 cpu_id=7 >>>>> <idle>-0 [007] d... 671.236046: cpu_idle: state=4294967295 cpu_id=7 >>>>> kworker/7:2-556 [007] .... 671.236073: cpu_frequency: state=3100000 cpu_id=7 >>>>> <idle>-0 [007] d... 671.236112: cpu_idle: state=4 cpu_id=7 >>>>> <idle>-0 [007] d... 671.393437: cpu_idle: state=4294967295 cpu_id=7 >>>>> ... >>>>> <idle>-0 [007] d... 671.401277: cpu_idle: state=4 cpu_id=7 >>>>> <idle>-0 [007] d... 671.404083: cpu_idle: state=4294967295 cpu_id=7 >>>>> kworker/7:2-556 [007] .... 671.404111: cpu_frequency: state=2900000 cpu_id=7 >>>>> <idle>-0 [007] d... 671.404125: cpu_idle: state=4 cpu_id=7 >>>>> <idle>-0 [007] d... 671.404974: cpu_idle: state=4294967295 cpu_id=7 >>>>> ... >>>>> <idle>-0 [007] d... 671.501180: cpu_idle: state=4 cpu_id=7 >>>>> <idle>-0 [007] d... 671.995414: cpu_idle: state=4294967295 cpu_id=7 >>>>> kworker/7:2-556 [007] .... 671.995459: cpu_frequency: state=2800000 cpu_id=7 >>>>> <idle>-0 [007] d... 671.995469: cpu_idle: state=4 cpu_id=7 >>>>> <idle>-0 [007] d... 671.996287: cpu_idle: state=4294967295 cpu_id=7 >>>>> ... >>>>> <idle>-0 [007] d... 672.001305: cpu_idle: state=4 cpu_id=7 >>>>> <idle>-0 [007] d... 672.078374: cpu_idle: state=4294967295 cpu_id=7 >>>>> kworker/7:2-556 [007] .... 672.078410: cpu_frequency: state=2600000 cpu_id=7 >>>>> <idle>-0 [007] d... 672.078419: cpu_idle: state=4 cpu_id=7 >>>>> <idle>-0 [007] d... 672.158020: cpu_idle: state=4294967295 cpu_id=7 >>>>> kworker/7:2-556 [007] .... 672.158040: cpu_frequency: state=2400000 cpu_id=7 >>>>> <idle>-0 [007] d... 672.158044: cpu_idle: state=4 cpu_id=7 >>>>> <idle>-0 [007] d... 672.160038: cpu_idle: state=4294967295 cpu_id=7 >>>>> ... >>>>> <idle>-0 [007] d... 672.234557: cpu_idle: state=4 cpu_id=7 >>>>> <idle>-0 [007] d... 672.237121: cpu_idle: state=4294967295 cpu_id=7 >>>>> kworker/7:2-556 [007] .... 672.237174: cpu_frequency: state=2100000 cpu_id=7 >>>>> <idle>-0 [007] d... 672.237186: cpu_idle: state=4 cpu_id=7 >>>>> <idle>-0 [007] d... 672.237778: cpu_idle: state=4294967295 cpu_id=7 >>>>> ... >>>>> <idle>-0 [007] d... 672.267902: cpu_idle: state=4 cpu_id=7 >>>>> <idle>-0 [007] d... 672.269860: cpu_idle: state=4294967295 cpu_id=7 >>>>> kworker/7:2-556 [007] .... 672.269906: cpu_frequency: state=1900000 cpu_id=7 >>>>> <idle>-0 [007] d... 672.269914: cpu_idle: state=4 cpu_id=7 >>>>> <idle>-0 [007] d... 672.271902: cpu_idle: state=4294967295 cpu_id=7 >>>>> ... >>>>> <idle>-0 [007] d... 672.751342: cpu_idle: state=4 cpu_id=7 >>>>> <idle>-0 [007] d... 672.823056: cpu_idle: state=4294967295 cpu_id=7 >>>>> kworker/7:2-556 [007] .... 672.823095: cpu_frequency: state=1600000 cpu_id=7 >>>>> >>>>> WITH >>>>> >>>>> <idle>-0 [007] dN.. 4380.928009: cpu_idle: state=4294967295 cpu_id=7 >>>>> kworker/7:2-399 [007] .... 4380.949767: cpu_frequency: state=2000000 cpu_id=7 >>>>> kworker/7:2-399 [007] .... 4380.969765: cpu_frequency: state=2200000 cpu_id=7 >>>>> kworker/7:2-399 [007] .... 4381.009766: cpu_frequency: state=2500000 cpu_id=7 >>>>> kworker/7:2-399 [007] .... 4381.029767: cpu_frequency: state=2600000 cpu_id=7 >>>>> kworker/7:2-399 [007] .... 4381.049769: cpu_frequency: state=2800000 cpu_id=7 >>>>> kworker/7:2-399 [007] .... 4381.069769: cpu_frequency: state=3000000 cpu_id=7 >>>>> kworker/7:2-399 [007] .... 4381.089771: cpu_frequency: state=3100000 cpu_id=7 >>>>> kworker/7:2-399 [007] .... 4381.109772: cpu_frequency: state=3400000 cpu_id=7 >>>>> kworker/7:2-399 [007] .... 4381.129773: cpu_frequency: state=3401000 cpu_id=7 >>>>> <idle>-0 [007] d... 4428.226159: cpu_idle: state=1 cpu_id=7 >>>>> <idle>-0 [007] d... 4428.226176: cpu_idle: state=4294967295 cpu_id=7 >>>>> <idle>-0 [007] d... 4428.226181: cpu_idle: state=4 cpu_id=7 >>>>> <idle>-0 [007] d... 4428.227177: cpu_idle: state=4294967295 cpu_id=7 >>>>> ... >>>>> <idle>-0 [007] d... 4428.551640: cpu_idle: state=4 cpu_id=7 >>>>> <idle>-0 [007] d... 4428.649239: cpu_idle: state=4294967295 cpu_id=7 >>>>> kworker/7:2-399 [007] .... 4428.649268: cpu_frequency: state=2800000 cpu_id=7 >>>>> <idle>-0 [007] d... 4428.649278: cpu_idle: state=4 cpu_id=7 >>>>> <idle>-0 [007] d... 4428.689856: cpu_idle: state=4294967295 cpu_id=7 >>>>> ... >>>>> <idle>-0 [007] d... 4428.799542: cpu_idle: state=4 cpu_id=7 >>>>> <idle>-0 [007] d... 4428.801683: cpu_idle: state=4294967295 cpu_id=7 >>>>> kworker/7:2-399 [007] .... 4428.801748: cpu_frequency: state=1700000 cpu_id=7 >>>>> <idle>-0 [007] d... 4428.801761: cpu_idle: state=4 cpu_id=7 >>>>> <idle>-0 [007] d... 4428.806545: cpu_idle: state=4294967295 cpu_id=7 >>>>> ... >>>>> <idle>-0 [007] d... 4429.051880: cpu_idle: state=4 cpu_id=7 >>>>> <idle>-0 [007] d... 4429.086240: cpu_idle: state=4294967295 cpu_id=7 >>>>> kworker/7:2-399 [007] .... 4429.086293: cpu_frequency: state=1600000 cpu_id=7 >>>>> >>>>> Without the patch the CPU dropped to min frequency after 3.2s >>>>> With the patch applied the CPU dropped to min frequency after 0.86s >>>>> >>>>> Signed-off-by: Stratos Karafotis <stratosk@semaphore.gr> >>>>> --- >>>>> v1 -> v2 >>>>> - Use correct terminology in change log >>>>> - Change the member variable name from 'deferred_periods' to 'idle_periods' >>>>> - Fix format issue >>>>> >>>>> drivers/cpufreq/cpufreq_conservative.c | 14 +++++++++++++- >>>>> drivers/cpufreq/cpufreq_governor.c | 18 +++++++++++++----- >>>>> drivers/cpufreq/cpufreq_governor.h | 1 + >>>>> 3 files changed, 27 insertions(+), 6 deletions(-) >>>>> >>>>> diff --git a/drivers/cpufreq/cpufreq_conservative.c b/drivers/cpufreq/cpufreq_conservative.c >>>>> index fa5ece3..d787772 100644 >>>>> --- a/drivers/cpufreq/cpufreq_conservative.c >>>>> +++ b/drivers/cpufreq/cpufreq_conservative.c >>>>> @@ -73,7 +73,19 @@ static unsigned int cs_dbs_update(struct cpufreq_policy *policy) >>>>> */ >>>>> if (cs_tuners->freq_step == 0) >>>>> goto out; >>>>> - >>>>> + /* >>>>> + * Decrease requested_freq for each idle period that we didn't >>>>> + * update the frequency >>>>> + */ >>>>> + if (policy_dbs->idle_periods < UINT_MAX) { >>>>> + unsigned int freq_target = policy_dbs->idle_periods * >>>>> + get_freq_target(cs_tuners, policy); >>>>> + if (requested_freq > freq_target) >>>>> + requested_freq -= freq_target; >>>>> + else >>>>> + requested_freq = policy->min; >>>>> + policy_dbs->idle_periods = UINT_MAX; >>>>> + } >>>>> /* >>>>> * If requested_freq is out of range, it is likely that the limits >>>>> * changed in the meantime, so fall back to current frequency in that >>>>> diff --git a/drivers/cpufreq/cpufreq_governor.c b/drivers/cpufreq/cpufreq_governor.c >>>>> index 3729474..1bc7137 100644 >>>>> --- a/drivers/cpufreq/cpufreq_governor.c >>>>> +++ b/drivers/cpufreq/cpufreq_governor.c >>>>> @@ -117,7 +117,7 @@ unsigned int dbs_update(struct cpufreq_policy *policy) >>>>> struct policy_dbs_info *policy_dbs = policy->governor_data; >>>>> struct dbs_data *dbs_data = policy_dbs->dbs_data; >>>>> unsigned int ignore_nice = dbs_data->ignore_nice_load; >>>>> - unsigned int max_load = 0; >>>>> + unsigned int max_load = 0, idle_periods = UINT_MAX; >>>>> unsigned int sampling_rate, io_busy, j; >>>>> >>>>> /* >>>>> @@ -163,8 +163,12 @@ unsigned int dbs_update(struct cpufreq_policy *policy) >>>>> * calls, so the previous load value can be used then. >>>>> */ >>>>> load = j_cdbs->prev_load; >>>>> - } else if (unlikely(time_elapsed > 2 * sampling_rate && >>>>> - j_cdbs->prev_load)) { >>>>> + } else if (unlikely(time_elapsed > 2 * sampling_rate)) { >>>>> + unsigned int periods = time_elapsed / sampling_rate; >>>>> + >>>>> + if (periods < idle_periods) >>>>> + idle_periods = periods; >>>>> + >>>>> /* >>>>> * If the CPU had gone completely idle and a task has >>>>> * just woken up on this CPU now, it would be unfair to >>>>> @@ -189,8 +193,10 @@ unsigned int dbs_update(struct cpufreq_policy *policy) >>>>> * 'time_elapsed' (as compared to the sampling rate) >>>>> * indicates this scenario. >>>>> */ >>>>> - load = j_cdbs->prev_load; >>>>> - j_cdbs->prev_load = 0; >>>>> + if (j_cdbs->prev_load) { >>>>> + load = j_cdbs->prev_load; >>>>> + j_cdbs->prev_load = 0; >>>>> + } >>>>> } else { >>>>> if (time_elapsed >= idle_time) { >>>>> load = 100 * (time_elapsed - idle_time) / time_elapsed; >>>>> @@ -218,6 +224,8 @@ unsigned int dbs_update(struct cpufreq_policy *policy) >>>>> if (load > max_load) >>>>> max_load = load; >>>>> } >>>>> + policy_dbs->idle_periods = idle_periods; >>>>> + >>>>> return max_load; >>>>> } >>>>> EXPORT_SYMBOL_GPL(dbs_update); >>>> >>>> I have a murky suspicion that the changes in dbs_update() are going to >>>> break something. I need to recall what it was, though. >>> >>> The only change in dbs_update() is the calculation of 'idle_periods'. >>> If I don't miss something I left current functionality untouched. >> >> Well, not quite. The else branch may now trigger when >> j_cdbs->prev_load is zero too which it didn't do before, AFAICS. > > What I mean is that the "if else" never triggers when > j_cdbs->prev_load is zero before the change, but that changes, so the > "else" branch will not cover the "j_cdbs->prev_load equal to zero" > case any more. I'm not sure how much that matters ATM, though.
Yes, I understood your point. You are absolutely right. The patch introduces a bug there:
If time_elapsed > 2 * sampling_rate, it calculates the idle_periods. Finally checks prev_load. If the prev_load equals to zero there is no load calculation at all.
Because, as you mentioned, the "else" branch will not cover this case.
So, we would have a load value only for the first deferred update and zero load if the update is deferred again.
> Sent too quickly, sorry.
I'm sorry for this mistake. My apologies. I will fix the patch and resend it.
Thanks, Stratos
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