TL;DR – the CPU is throttled to ~60% during Lightroom exports, no such throttling during heavy load tests with other apps.
Details:
Lightroom Classic is what I primarily use my computer for, so when I received my 16" M3 Max 14c, I was disappointed in the test I ran (a series of 500 Sony A1 images, exported to JPEGs)... it was better than the M1 Max, but not nearly as much as I was expecting. The M1 Max did the job in 9:37, while the M3 Max took 8:59. Later, I repeated the test, and got varied results in the 6-8 minute range. Observing the temperature and CPU/GPU load data, a fairly predictable pattern is visible:
1) It starts out with both the CPU and GPU running strong... images are exported at a rate of about 2 per second
2) Temperature rapidly starts to increase, reaching about 100C after 30-60 seconds
3) Fans start to ramp up, temperature begins to come down
4) CPU usage drops dramatically, to about 20% (though on some runs this stage would be 40-60%), GPU drops a bit, temperature drops to 60-70C, fans spin down, export rate slows to under 1 per second
5) After a few minutes in that state, CPU usage tentatively starts to increase to 70-90%, temperature slowly increases in turn, but no noticeable fan increase
6) As temperature reaches about 85C, CPU usage drops to around 60%, where it seems to reach somewhat of an equilibrium, with the GPU in the 80% range, still no audible fan... export rate has leveled off at about 1 per second
Now, one run finished in a mere 4:39(!)... that one was done first thing this morning, when the computer was completely cold, which presumably enabled it to stay at a higher CPU usage for longer (for the other runs, I let it cool down to an idle temperature of 50-60C). So, this seems like this is thermal throttling, right? Heavy load, computer gets hot, CPU throttles.
A few mysteries though. When it reaches that "equilibrium" state, the fans are not audibly running, so it's got plenty of headroom to accommodate more load.
Secondly, running another test that consisted of a video export from FCPX (mostly GPU) along with another app to put an additional load on the CPU, it behaved more like you would expect it to... temperature around 100-105C, fans running, CPU and GPU both pegged, and it stayed in this consistent state indefinitely. If the Lightroom scenario was the system throttling, why did similar throttling not also occur during this other test? Or, to put it differently, if it can handle this heavy stress test without significant throttling (or even if it is throttling a bit, it's at least TRYING to keep performance up by running the fans), why didn't it do so during the Lightroom export?
One other observation... while this export is going on (with LR's CPU usage staying around 60%) if I then initiate a "build previews" in LR, the CPU usage pegs again, and stays there (with fans spinning up). So, the capacity is there, just for some reason LR is not using it continuously during export.
High power mode doesn't make an appreciable difference... if there's any improvement, it's small enough to be lost in the variability of each test.
Lastly, briefly going back to the M1 Max, I do see similar behavior, but not as severe as this (need to run some more tests on that machine though, I've been focused mainly on the M3).
Details:
Lightroom Classic is what I primarily use my computer for, so when I received my 16" M3 Max 14c, I was disappointed in the test I ran (a series of 500 Sony A1 images, exported to JPEGs)... it was better than the M1 Max, but not nearly as much as I was expecting. The M1 Max did the job in 9:37, while the M3 Max took 8:59. Later, I repeated the test, and got varied results in the 6-8 minute range. Observing the temperature and CPU/GPU load data, a fairly predictable pattern is visible:
1) It starts out with both the CPU and GPU running strong... images are exported at a rate of about 2 per second
2) Temperature rapidly starts to increase, reaching about 100C after 30-60 seconds
3) Fans start to ramp up, temperature begins to come down
4) CPU usage drops dramatically, to about 20% (though on some runs this stage would be 40-60%), GPU drops a bit, temperature drops to 60-70C, fans spin down, export rate slows to under 1 per second
5) After a few minutes in that state, CPU usage tentatively starts to increase to 70-90%, temperature slowly increases in turn, but no noticeable fan increase
6) As temperature reaches about 85C, CPU usage drops to around 60%, where it seems to reach somewhat of an equilibrium, with the GPU in the 80% range, still no audible fan... export rate has leveled off at about 1 per second
Now, one run finished in a mere 4:39(!)... that one was done first thing this morning, when the computer was completely cold, which presumably enabled it to stay at a higher CPU usage for longer (for the other runs, I let it cool down to an idle temperature of 50-60C). So, this seems like this is thermal throttling, right? Heavy load, computer gets hot, CPU throttles.
A few mysteries though. When it reaches that "equilibrium" state, the fans are not audibly running, so it's got plenty of headroom to accommodate more load.
Secondly, running another test that consisted of a video export from FCPX (mostly GPU) along with another app to put an additional load on the CPU, it behaved more like you would expect it to... temperature around 100-105C, fans running, CPU and GPU both pegged, and it stayed in this consistent state indefinitely. If the Lightroom scenario was the system throttling, why did similar throttling not also occur during this other test? Or, to put it differently, if it can handle this heavy stress test without significant throttling (or even if it is throttling a bit, it's at least TRYING to keep performance up by running the fans), why didn't it do so during the Lightroom export?
One other observation... while this export is going on (with LR's CPU usage staying around 60%) if I then initiate a "build previews" in LR, the CPU usage pegs again, and stays there (with fans spinning up). So, the capacity is there, just for some reason LR is not using it continuously during export.
High power mode doesn't make an appreciable difference... if there's any improvement, it's small enough to be lost in the variability of each test.
Lastly, briefly going back to the M1 Max, I do see similar behavior, but not as severe as this (need to run some more tests on that machine though, I've been focused mainly on the M3).
