Participant

Lightroom Classic 15.4.1: export caps P-cores at 2.4GHz on M5 Pro (macOS 26)

Forum|Forum|11 hours ago
July 17, 2026
2 replies
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# Environment
- Mac: MacBook Pro 14" 2026, M5 Pro (18-core) (identifier: Mac17,9)
- RAM: 64 GB
- macOS: 26.5.1 (build 25F80)
- Lightroom Classic: 15.4.1 (latest)
- Power: AC connected, High Power Mode enabled (powermode 2)
- Catalog: freshly created; source files and export destination both on internal SSD
- Previous machine for comparison: MacBook Pro (M1 Pro)

# Symptom
During export, total CPU utilization plateaus around 50% and exports are much slower
than expected. Using powermetrics, I confirmed that while exporting, the P-cores
(P0 cluster) are ~100% active but locked at roughly 2.4 GHz (2304-2652 MHz),
never boosting above 3 GHz. The P1 cluster stays mostly idle.

Measured comparison against M1 Pro (same photos, same export settings):
- Export: 92 s on M1 Pro -> 70 s on M5 Pro (only ~24% faster)
- AI Denoise: 9.5 s on M1 Pro -> 4.5 s on M5 Pro (~2.1x faster)
GPU/Neural Engine-bound tasks like Denoise scale as expected with the new chip,
while the CPU-bound export barely improves. Also, on the M1 Pro all cores were
fully utilized during export, whereas on the M5 Pro the P-cores are frequency-capped
as described above. This looks like a regression in export behavior across
chip generations.

# What I have ruled out
1. Thermal throttling: thermal pressure stays "Nominal" during export
(powermetrics --samplers thermal)
2. Low Power Mode: off (High Power Mode is enabled)
3. Background apps: reproduced with all third-party background apps quit
4. App Nap: disabled via NSAppSleepDisabled
5. taskpolicy -B applied to the Lightroom process: no change
6. Splitting the export into multiple simultaneous batches: CPU usage did not increase
7. Hardware sanity check: on the same machine, a synthetic CPU load test
unrelated to Lightroom (running 12 instances of "yes > /dev/null" in Terminal
to load all P-cores at 100%) boosts the P-cores to 4.2-4.4 GHz with thermal
pressure still Nominal. This confirms the chip, cooling, and power settings
are all healthy - the frequency cap only occurs during Lightroom exports.

# Conclusion (hypothesis)
The export worker threads appear to be created with a background/low QoS class,
so macOS runs them at reduced clock speeds even though the cores are available.
This matches reports in this thread:
https://community.adobe.com/t5/lightroom-classic-discussions/why-does-lightroom-not-use-the-performance-cores-m4max-during-export/td-p/15349358

# Request
Please review the QoS/priority of the export worker threads so that Apple Silicon
P-cores can run at their normal frequencies during export. I can provide full
powermetrics logs on request.

# Reference data
- During Lightroom export: P0 cluster averages ~2005-2449 MHz at 90-100% utilization
- Synthetic CPU load test: P0 cluster averages 3568 MHz (~53% residency at
4308-4380 MHz), P1 cluster averages 4002 MHz

T

TKAuthor

Participant

Here's an excerpt from the log.

--- During Lightroom export ---
P0-Cluster HW active frequency: 2431 MHz
P0-Cluster HW active residency: 40.88% (1344 MHz: .18% 1644 MHz: 0% 1992 MHz: 5.9% 2304 MHz: 14% 2652 MHz: 20% 2964 MHz: 0% 3240 MHz: 0% 3504 MHz: 0% 3696 MHz: 0% 3876 MHz: 0% 4044 MHz: 0% 4176 MHz: 0% 4284 MHz: 0% 4308 MHz: .05% 4380 MHz: 0%)
P1-Cluster HW active frequency: 2505 MHz
P1-Cluster HW active residency: 100.00% (1344 MHz: 0% 1644 MHz: 0% 1992 MHz: 11% 2304 MHz: 16% 2652 MHz: 73% 2964 MHz: .14% 3240 MHz: 0% 3504 MHz: 0% 3696 MHz: 0% 3876 MHz: 0% 4044 MHz: 0% 4176 MHz: 0% 4284 MHz: 0% 4308 MHz: .24% 4380 MHz: 0%)
CPU Power: 13166 mW
Current pressure level: Nominal

--- Synthetic load (12x yes) ---
P0-Cluster HW active frequency: 4372 MHz
P0-Cluster HW active residency: 97.84% (1344 MHz: 0% 1644 MHz: 0% 1992 MHz: 0% 2304 MHz: .33% 2652 MHz: 0% 2964 MHz: 0% 3240 MHz: 0% 3504 MHz: 0% 3696 MHz: 0% 3876 MHz: 0% 4044 MHz: 0% 4176 MHz: 0% 4284 MHz: 0% 4308 MHz: 1.4% 4380 MHz: 96%)
P1-Cluster HW active frequency: 4346 MHz
P1-Cluster HW active residency: 100.00% (1344 MHz: 0% 1644 MHz: 0% 1992 MHz: 0% 2304 MHz: .17% 2652 MHz: 0% 2964 MHz: 0% 3240 MHz: 0% 3504 MHz: 0% 3696 MHz: 0% 3876 MHz: 0% 4044 MHz: 0% 4176 MHz: 0% 4284 MHz: 7.1% 4308 MHz: 33% 4380 MHz: 60%)
CPU Power: 12850 mW
Current pressure level: Nominal

M

moana75sin

Participant

Hello,
@TK
Thanks for providing such a thorough investigation. You've ruled out the common causes—thermal limits, power settings, storage, and hardware and the comparison with a synthetic CPU workload is especially compelling. The fact that AI Denoise scales as expected while exports remain frequency-limited suggests this is likely specific to Lightroom Classic's export pipeline rather than an Apple Silicon or macOS issue. Your QoS/thread-priority hypothesis seems plausible, particularly since the P-cores can reach full boost under other CPU-intensive workloads. Hopefully Adobe's engineering team can review the export worker scheduling and compare it against newer Apple Silicon architectures. Sharing your powermetrics logs with Adobe could provide valuable data to help reproduce and diagnose the issue. login Illinois Tollway

T

TKAuthor

Participant

@moana75sin

Thanks for the comment.
I've added an excerpt from the log.

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