Gadfu
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DELL XPS 15 9550 - CPU speed cap on battery

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So, as most 9550 owners, who watch this forums probably know, the recent BIOS update 1.1.15 is supposed to fix CPU Speed cap after pulling the AC cable. People in another thread stated, that their processors now run at full turbo on battery. 

However my CPU still runs at 1.69GHz max on battery after the BIOS update, while the base clock of the 6700HQ should be 2.6GHz. Plugging in the AC cable now instantly goes back to full turbo, which is fine.

What makes this worse, is that the CPU clock under battery and load climbs painfully slowly towards the 1.69GHz mark, starting at 0.6GHz and taking 20 Seconds to reach 1.69GHz. This still only happens, when pulling the AC cable while the system is running. When im booting freshly on battery it jumps instantly to 1.69GHz under load.

My config is: UHD Disply, 6700HQ, 512GB SSD (PM951), 16GB RAM, BIOS Version: 1.1.15

Is anyone else still having these issues after BIOS 1.1.15?

Thanks alot folks

Edit:
Also when stressing the CPU, Windows logs show "the speed of processor 1 in group 0 is being limited by system firmware" for each logical core, no matter if booted on battery or pulling the plug afterwards. 

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delliberate
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RE: DELL XPS 15 9550 - CPU speed cap on battery

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I just had the same thing on a 9560 with the latest firmware / BIOS.  My cap was at 28x multipllier, so not massive but enough to cripple my audio DAW performance at high CPU demands.

Turns out it was caused by undervolting the CPU cache!  I applied a typical -120mv offset to both CPU core and cache using Throttlestop.  The cache offset caused the multiplier limit on battery - removing it (CPU core offset can stay in place) allowed me to hit the 34x multiplier on battery.

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james.monsen
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RE: DELL XPS 15 9550 - CPU speed cap on battery

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You need to go to the Device Manager and click on Firmware.  Then right click on the System Firmware and choose Update Driver Software.  Finally choose Search Automatically.... and you should see the huge improvement in performance that comes along with 1.1.15.

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delliberate
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RE: DELL XPS 15 9550 - CPU speed cap on battery

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I just had the same thing on a 9560 with the latest firmware / BIOS.  My cap was at 28x multipllier, so not massive but enough to cripple my audio DAW performance at high CPU demands.

Turns out it was caused by undervolting the CPU cache!  I applied a typical -120mv offset to both CPU core and cache using Throttlestop.  The cache offset caused the multiplier limit on battery - removing it (CPU core offset can stay in place) allowed me to hit the 34x multiplier on battery.

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delliberate
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RE: DELL XPS 15 9550 - CPU speed cap on battery

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.. and interestingly it also avoids the very slow stepping up of the multiplier when you first pull AC.

Seems like the CPU very carefully monitors its various voltage demands and automatically compensates to keep the system stable.  Impressive.

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