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Don’t Trust Activity Monitor on M1 Macs

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Re: Don’t Trust Activity Monitor on M1 Macs

#11

Post by mattnewton »

lkxijlewlf wrote: post #8
tmikaeld wrote: post #3

Earlier quoted context omitted.

Since Apple have full control over each Mac's hardware, couldn't they within a quite narrow average know how much power is consumed? You also have hardware control chips like the T1/T2 that could help narrow this down even further. I would get it for PC's, but here, it's quite different.

Yes. But why would they? There's no benefit for them.

A lot of reasons to profile this if you want to advertise battery life. Internally it let's you collect metrics on apps threatening your battery life promises and externally it gives the consumers the ability to accurately blame apps when they get lower than expected battery life. For example they can notice that safari uses less power than chrome or that final cut uses way more power than they expected, etc etc

Re: Don’t Trust Activity Monitor on M1 Macs

#12

Post by jeffbee »

tmikaeld wrote: post #3
jeroenhd wrote: post #2

I don't get it. CPU graphs don't show power usage and they never have; they show how much time, percentually, a CPU was busy executing a certain type of task. You can never get a power estimate from a CPU usage graph at all. Even during normal operation purely on performance cores the clock speed will go up and down as the OS idles or new tasks get spawned. Whatever 10% is in your graph changes depending on the state…

Since Apple have full control over each Mac's hardware, couldn't they within a quite narrow average know how much power is consumed? You also have hardware control chips like the T1/T2 that could help narrow this down even further. I would get it for PC's, but here, it's quite different.

They wouldn’t need to guess. CPUs measure their own current consumption and demand specific voltage levels from their regulators. They know the instantaneous power consumption to at least three significant digits.

Re: Don’t Trust Activity Monitor on M1 Macs

#13

Post by wongarsu »

tmikaeld wrote: post #3
jeroenhd wrote: post #2

I don't get it. CPU graphs don't show power usage and they never have; they show how much time, percentually, a CPU was busy executing a certain type of task. You can never get a power estimate from a CPU usage graph at all. Even during normal operation purely on performance cores the clock speed will go up and down as the OS idles or new tasks get spawned. Whatever 10% is in your graph changes depending on the state…

Since Apple have full control over each Mac's hardware, couldn't they within a quite narrow average know how much power is consumed? You also have hardware control chips like the T1/T2 that could help narrow this down even further. I would get it for PC's, but here, it's quite different.

On Windows (or Linux) you can get power consumption numbers down to the core using tools like HWMonitor. My CPU is currently using 95W, and my GPU uses 15W. Of course then you have fans, motherboard etc. On server hardware (where software-queriable power meters in the power supply are commonplace) having as much power draw from the fans as from the CPU isn't uncommon.

Re: Don’t Trust Activity Monitor on M1 Macs

#14

Post by avianlyric »

dijit wrote: post #5

I'm torn, or maybe I misunderstood, from what I know about energy efficiency of CPU's, it has always been: Spend less time on the CPU. If your task is short lived, or constrained by I/O, affining it to E cores is going to be better so that you don't have to "race to a stop-light". But, to take an extreme example: having a 10w CPU awake for 24hrs vs a 30w one for 7 hours is going to be less energy efficient.

Race-to-idle is a good strategy in homogenous CPU setups.

But chips like the M1 with its E and P cores (or ARMs BIG.little designs) significantly change the playing field, and race-to-idle makes less sense.

Two of the places you can look to understand why running on an E core for longer is better than running on a P core for shorter, is power consumption as frequency increases, and number of computational units in each core.

Power consumption in CPU generally increases exponentially with clock frequency. So double the frequency, if 4x the power (as a very rough guiding principle), so going slow and steady can be more power efficient.

Additionally E cores will have fewer computational units (ALUs and other basic computing blocks) compared to a P core. Running a core generally means you’re powering all of it computational units, regardless of if they’re actually doing any work (modern CPU have very good power gating, but there’s a limit). So running a core with less silicon is more efficient, because portion of powered silicon doing useful work is larger.

Put all of the above together, throw in sophisticated power gating, CPU clock scaling, various on die peripherals (like media engines, crypto engines etc) and all of a sudden, simple strategies like race-to-idle stop being a good approach.

Re: Don’t Trust Activity Monitor on M1 Macs

#15

Post by avianlyric »

tmikaeld wrote: post #3
jeroenhd wrote: post #2

I don't get it. CPU graphs don't show power usage and they never have; they show how much time, percentually, a CPU was busy executing a certain type of task. You can never get a power estimate from a CPU usage graph at all. Even during normal operation purely on performance cores the clock speed will go up and down as the OS idles or new tasks get spawned. Whatever 10% is in your graph changes depending on the state…

Since Apple have full control over each Mac's hardware, couldn't they within a quite narrow average know how much power is consumed? You also have hardware control chips like the T1/T2 that could help narrow this down even further. I would get it for PC's, but here, it's quite different.

They do, and their software knows as well. It’s just Activity Monitor that isn’t currently using the data for some reason.

Re: Don’t Trust Activity Monitor on M1 Macs

#16

Post by cuu508 »

wongarsu wrote: post #13
tmikaeld wrote: post #3

Earlier quoted context omitted.

Since Apple have full control over each Mac's hardware, couldn't they within a quite narrow average know how much power is consumed? You also have hardware control chips like the T1/T2 that could help narrow this down even further. I would get it for PC's, but here, it's quite different.

On Windows (or Linux) you can get power consumption numbers down to the core using tools like HWMonitor. My CPU is currently using 95W, and my GPU uses 15W. Of course then you have fans, motherboard etc. On server hardware (where software-queriable power meters in the power supply are commonplace) having as much power draw from the fans as from the CPU isn't uncommon.

Where is HWMonitor getting this data from?

> My CPU is currently using 95W

Are you currently stressing the CPU (compiling, rendering, ...)? If you are not, the 95W figure seems suspect. (FWIW, my entire system, fans and all, uses 25W at the wall when idle. The CPU is Intel 9700k, no dGPU).

Re: Don’t Trust Activity Monitor on M1 Macs

#18

Post by throwaway09223 »

wongarsu wrote: post #13
tmikaeld wrote: post #3

Earlier quoted context omitted.

Since Apple have full control over each Mac's hardware, couldn't they within a quite narrow average know how much power is consumed? You also have hardware control chips like the T1/T2 that could help narrow this down even further. I would get it for PC's, but here, it's quite different.

On Windows (or Linux) you can get power consumption numbers down to the core using tools like HWMonitor. My CPU is currently using 95W, and my GPU uses 15W. Of course then you have fans, motherboard etc. On server hardware (where software-queriable power meters in the power supply are commonplace) having as much power draw from the fans as from the CPU isn't uncommon.

> power consumption numbers down to the core using tools like HWMonitor.

These are just rough estimates and can be wildly inaccurate (just like in the OSX post we're discussing). AFAIK there's no facility for actual measurement.

> On server hardware (where software-queriable power meters in the power supply are commonplace)

Are you certain these are actual meters and not just estimates done in software?

Re: Don’t Trust Activity Monitor on M1 Macs

#19

Post by wongarsu »

cuu508 wrote: post #16
wongarsu wrote: post #13

Earlier quoted context omitted.

On Windows (or Linux) you can get power consumption numbers down to the core using tools like HWMonitor. My CPU is currently using 95W, and my GPU uses 15W. Of course then you have fans, motherboard etc. On server hardware (where software-queriable power meters in the power supply are commonplace) having as much power draw from the fans as from the CPU isn't uncommon.

Where is HWMonitor getting this data from? > My CPU is currently using 95W Are you currently stressing the CPU (compiling, rendering, ...)? If you are not, the 95W figure seems suspect. (FWIW, my entire system, fans and all, uses 25W at the wall when idle. The CPU is Intel 9700k, no dGPU).

It's a desktop with a 24 core Threadripper with a 250W TPD, not designed for efficiency at all. Probably something or another was using 2 to 6 cores.

Re: Don’t Trust Activity Monitor on M1 Macs

#20

Post by mc4ndr3 »

There's an argument that says to prefer performance cores, because once a non-looping task completes, the cores can idle again.

This allows the system to more quickly reach a very power efficient state, compared to leaving a weak stove on to cook a large pot of chili.

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