[SOLVED] Is this normal behaviour of Intel low power (U) processors?

[bladteth]

Hi,

I've noticed that when running on battery, i5-5300U CPU clock in Dell E7450 is very slow to ramp up when at full load. It idles at 800 MHz and when stress test is initiated (or any other heavy load) it takes about 10 seconds for the clock to start increasing and about 30 seconds to reach full boost of 2.7 GHz. This is not the case when laptop runs on AC power - CPU clock goes up to full boost almost instantly. I've checked my wife's E5550, which runs on i5-4310U and the CPU behaves in the same manner. 'Standard' power CPUs in other laptops in the household (i7-3610QM and i7-6700HQ) do not exhibit this phenomenon and both ramp up clocks straight away whether on battery or AC power. Is this something specific to U processors? Or perhaps Dell's laptops? Is there any way to disable this 'feature'?

Thanks.

 

[Aeacus]

Looks like a normal behavior. Since when on battery power, PC knows that and won't boost up the U-suffix CPU to the max at instant. Instead, it's gradual to save battery. But on AC power, there's no need to save battery and CPU boost works normal.

AFAIK, this "feature" is unique to U-suffix CPUs. And if you don't like this, don't get the laptop with U-suffix CPU in the first place. There is no "disable" of this feature, as far as i know.

 

[bladteth]

Thanks Aeacus. Interestingly, the initial delay only happens after unplugging AC. Once full boost is reached and laptop goes back to idle, the clock fluctuates around 1 GHz. Afterwards, when loaded again, it ramps up quickly, just like on AC power... until next time AC is plugged in and unplugged, which seems to reset the cycle. Also, when disconnecting AC, ThrottleStop displays BD PROCHOT for about 3 seconds during which time CPU clock is limited to 500 MHz temporarily. Works fine afterwards. This happens on both laptops. I don't mind this behaviour particularly and was just curious.

 

[Nighthawk117]

Hi,

I've noticed that when running on battery, i5-5300U CPU clock in Dell E7450 is very slow to ramp up when at full load. It idles at 800 MHz and when stress test is initiated (or any other heavy load) it takes about 10 seconds for the clock to start increasing and about 30 seconds to reach full boost of 2.7 GHz. This is not the case when laptop runs on AC power - CPU clock goes up to full boost almost instantly. I've checked my wife's E5550, which runs on i5-4310U and the CPU behaves in the same manner. 'Standard' power CPUs in other laptops in the household (i7-3610QM and i7-6700HQ) do not exhibit this phenomenon and both ramp up clocks straight away whether on battery or AC power. Is this something specific to U processors? Or perhaps Dell's laptops? Is there any way to disable this 'feature'?

Thanks.

What power profile are you using? Mine doesn't behave like that but I have 8th gen, 6th gen and above have SpeedShift so they ramp up and down more quickly anyway.

 

[bladteth]

What power profile are you using? Mine doesn't behave like that but I have 8th gen, 6th gen and above have SpeedShift so they ramp up and down more quickly anyway.

I tried all different power profiles and power settings, and it made no difference. As you said Speed Shift is not available in 5th gen and older CPUs. I can set clock 'aggressiveness' via Speed Shift settings in ThrottleStop in my laptop with i7-6700HQ, but this option is unavailable in both 4310U and 5300U.

 

[Nighthawk117]

I tried all different power profiles and power settings, and it made no difference. As you said Speed Shift is not available in 5th gen and older CPUs. I can set clock 'aggressiveness' via Speed Shift settings in ThrottleStop in my laptop with i7-6700HQ, but this option is unavailable in both 4310U and 5300U.

I don't have a machine older than 6th gen so I don't know if it's normal behaviour for the U chips themselves or just a quirk of the Dell laptops. I doubt there is anything you can do about it though.

 

[uWebb429]

when disconnecting AC, ThrottleStop displays BD PROCHOT for about 3 seconds

This type of throttling is by design. It helps protect the battery from any sudden changes in power consumption. BD PROCHOT throttling is not a problem if it is only happening for a few seconds during the transition to battery power.

Are you using any Dell power management software on your computer? Have you tried using ThrottleStop to access the Windows High Performance power plan while running on battery power? This might improve responsiveness. Post a screenshot of ThrottleStop while using this power plan while your laptop is unplugged and running on battery power. Older laptops that do not use Speed Shift Technology are not nearly as responsive off idle compared to newer laptops that do use this technology.

I run my 4th Gen laptop at full speed while on battery power. No lack of off idle responsiveness.

Intel CPUs do most of their power saving when unused cores enter the low power C7 - C state. An idle CPU at 3200 MHz does not consume 4X as much power as an idle CPU at 800 MHz. Idle cores are spending most of their time in C7 where they are disconnected from the internal clock and sitting dormant at 0 MHz. The speed of the active cores does not make a big difference to power consumption when a CPU is idle.

 

[bladteth]

This type of throttling is by design. It helps protect the battery from any sudden changes in power consumption. BD PROCHOT throttling is not a problem if it is only happening for a few seconds during the transition to battery power.

This is not the case in my i7-6700HQ, which switches to battery mode with no hick-up at all.

Are you using any Dell power management software on your computer? Have you tried using ThrottleStop to access the Windows High Performance power plan while running on battery power? This might improve responsiveness.

No Dell power management. It makes no difference to delay whether TS is set to Balanced or High Performance. Even in HP mode, clock hesitates to go up initially, but after some 30 seconds reaches full boost.

I run my 4th Gen laptop at full speed while on battery power. No lack of off idle responsiveness.

Yours is 'full fat', 47W CPU, not low power U one. The other laptop I've got, which runs on i7-3610QM (45W) also doesn't hesitate to reach full boost clock and power immediately.

Intel CPUs do most of their power saving when unused cores enter the low power C7 - C state. An idle CPU at 3200 MHz does not consume 4X as much power as an idle CPU at 800 MHz. Idle cores are spending most of their time in C7 where they are disconnected from the internal clock and sitting dormant at 0 MHz. The speed of the active cores does not make a big difference to power consumption when a CPU is idle.

That's correct. What seems to be a workaround is to disable SpeedStep. In this mode CPU operates at almost max clock, but since C0 is lower, total power draw is pretty much the same as in 800 MHz state with SS active, and there is no delay when full power is required.

 

[uWebb429]

This is not the case in my i7-6700HQ

Not all manufacturers use the BD PROCHOT throttling technique when switching to battery power. If you think this safety feature is really not necessary, using ThrottleStop to disable BD PROCHOT should prevent this from happening.

In Power Options I would press the Restore plan defaults button for each of your power plans.

When using ThrottleStop on older CPUs, try checking the Set Multiplier box so this information is sent to the CPU.

You can also try setting the Non Turbo Ratio to a value of 1.

In the TPL window, try checking the MMIO Lock box. Watch what the reported power limits are at the top of this window while your CPU is loaded. Dell engineering have dreamed up a lot of bizarre throttling schemes over the years. Your CPU might get stuck at 800 MHz because a power limit is set too low. Power limits can be changed dynamically over time which is why I am thinking that Dell might be using this control method.

It is very unusual for a CPU not to jump up to max speed as soon as a significant load is detected. Post a screenshot of the TPL window so I can see what other options are available to control this.

Does the Limit Reasons window show any throttling reasons when your CPU is loaded and stuck at 800 MHz?

 

[bladteth]

In Power Options I would press the Restore plan defaults button for each of your power plans.

Restoring power plans did not make any difference. Set Multiplier (even with Power Saver) or Non Turbo Ratio methods both worked. Power limits are set to default and actually never reached, even under full load (check previous links to screenshots). Looks like there are a few workarounds. Thanks for your help.