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C
chfilm
Inspiring
May 31, 2025
Answered

Why does Lightroom not use the performance cores (M4Max) during export??

  • May 31, 2025
  • 1 reply
  • 2153 views

Hi,

I was wondering if anyone could shed some light on why Lightroom Classic (14.3.1) doesnt seem to use the performance cores of my m4max macbook pro AT ALL during export? it's slowly chugging along on the 4 efficiency cores, while the real workhorses sit idle. 

The Gpu is not maxed out either, nor is the Ram. 

 

I found many sources stating this behavior on the m4 macbook air, but couldn't really find sources about the macbook pro and find this really odd. Anybody else noticed this?

    Correct answer chfilm

    [This post contains formatting and embedded images that don't appear in email. View the post in your Web browser.]

     

    Very interesting. I observed the same behavior on my Macbook M2 Max exporting 1000 raws from and to the internal SSD:

    (See the attached spreadsheet.)

     

    After 364 files, the Mac throttled back on the GPU and performance cores. (Maybe the GPU was throttled and the performance cores were limited by that; or maybe the performance cores were throttled, and the GPU limited by that; or maybe both were throttled.)

     

    Overall, keeping the fans on increased the rate of export by 23%.  But just comparing the time when the GPU and cores were throttled (after the first 364 files), the rate of export was 41% faster with the fans on.

     

    * * *

     

    I don't think this is under the direct control of LR (or any typical app). It's the operating system and firmware that decide when to throttle.

     

    * * *

     

    I didn't think there were thermal issues with the Apple Silicon Macbook Pros. The last years of the Intel Macbook Pros were notorious for their bad thermal engineering, with throttled CPUs due to overheating and fans that got easily  clogged.

     

    It may be that the Apple designers have deliberately chosen to run the fans less aggressively in order to keep the Macbooks quieter. Many people really don't like to hear the fans running (like my wife).

     

     

     


    Hey, I did another test while actually measuring the time difference and it's crazy! 
    650 pics export with the standard mac os fan control: 13 minutes.

    The same run but with manual fan control: 7:30 minutes! 

     

    So almost twice as fast!! 

    Something can't be right here? I think the fans used to spin up by themselves eventually but now, not at all! Only during GPU only tasks..

    1 reply

    johnrellis
    johnrellis
    Legend
    June 2, 2025

    [This post contains formatting and embedded images that don't appear in email. View the post in your Web browser.]

     

    By default on newer hardware, the GPU does all the heavy computation for Export, and the CPU cores do all the lighter-weight bookkeeping.  So in your instance, running the CPU threads on efficiency cores is sufficient to keep up with the GPU.

     

    If the GPU isn't being maxed out, there could be other limiting factors, e.g. reading the source photos from a slow disk or network volume or writing the exported photos to slow destination disk.

     

    1. Do the LR menu command Help > System Info and copy/paste the entire contents here so we can see exactly which versions of hardware and software LR thinks you're running and important LR options that are set.

     

    2. Select several dozen raws and start an export.  After it's been running for 30 seconds or more, post a screenshot of Activity Monitor showing CPU History and GPU History, e.g. 

     

     

     

     

    C
    chfilmAuthor
    Inspiring
    June 8, 2025

    Pretext: all photos are on a samsung 4TB SSD capable of 1000mb/s.

     

    It's very interesting, I did some more testing..  and I found that it seems to be some sort of thermal throttling behavior that's going on.. The first 230 images or so get exported super fast, also using all cores pretty fully. But when I then went on to export another 600 images, I saw the same odd behavior again of only the efficiency cores being maxed out while the rest is at 30-40% utilization. Same for the GPU. I then manually ramped up the fans (which were almost unnoticable up to this point) and oh voila- suddenly, the cpus are working much harder again too! 

    What kind of brought me on this track was that I watched a review of the m4 macbook air, which doesnt have active cooling, and shows the exact same behavior after a short time of LR exporting. But I find it really super odd that my macbook doesnt ramp up the fans by itself to give the CPU more headroom to use its full potential. Especially since the fans ARE spinning super loudly by themselves when I do something like AI retouching with Arams that uses the GPU to it's maximum. The fans are at absolute full blast right now while the gpu is crunching... 

     

    Can that be something LR related or is that more like a problem with my specific machine or Mac OS even? 

     

    Please have a loot at the attached screenshots, and find below the log:

     

    Lightroom Classic version: 14.3.1 [ 202505061331-b063faef ]
    License: Creative Cloud
    Language setting: en
    Operating system: Mac OS 15
    Version: 15.5.0 [24F74]
    Application architecture: arm64
    Logical processor count: 14
    Processor speed: NA
    SqLite Version: 3.36.0
    Power Source: Plugged In, 75%, Charging
    Built-in memory: 36.864,0 MB
    Dedicated GPU memory used by Lightroom: 395,5MB / 27.648,0MB (1%)
    Real memory available to Lightroom: 36.864,0 MB
    Real memory used by Lightroom: 2.446,1 MB (6,6%)
    Virtual memory used by Lightroom: 414.904,6 MB
    Memory cache size: 3.661,2MB
    Internal Camera Raw version: 17.3.1 [ 2227 ]
    Maximum thread count used by Camera Raw: 5
    Camera Raw SIMD optimization: SSE2
    Camera Raw virtual memory: 188MB / 18431MB (1%)
    Camera Raw real memory: 190MB / 36864MB (0%)

    Cache1:
    NT- RAM:0,0MB, VRAM:0,0MB, Combined:0,0MB

    Cache2:
    m:3.661,2MB, n:0,0MB

    U-main: 126,0MB

    Standard Preview Size: 2880 pixels
    Displays: 1) 5120x2880, 2) 3024x1964

    Graphics Processor Info:
    Metal: Apple M4 Max
    Init State: GPU for Export supported by default
    User Preference: Auto
    Enable HDR in Library: OFF

    Application folder: /Applications/Adobe Lightroom Classic
    Library Path: /Volumes/4TB SSD/01_Lightroom/Lightroom Catalog-v13-3.lrcat
    Settings Folder: /Users/Nastya/Library/Application Support/Adobe/Lightroom

    Installed Plugins:
    1) AdobeStock
    2) Aperture/iPhoto Importer Plug-in
    3) Flickr
    4) Logi Plugin
    5) Retouch4me Arams

    Config.lua flags:

     

     

    johnrellis
    johnrellis
    Legend
    June 8, 2025

    [This post contains formatting and embedded images that don't appear in email. View the post in your Web browser.]

     

    Very interesting. I observed the same behavior on my Macbook M2 Max exporting 1000 raws from and to the internal SSD:

    (See the attached spreadsheet.)

     

    After 364 files, the Mac throttled back on the GPU and performance cores. (Maybe the GPU was throttled and the performance cores were limited by that; or maybe the performance cores were throttled, and the GPU limited by that; or maybe both were throttled.)

     

    Overall, keeping the fans on increased the rate of export by 23%.  But just comparing the time when the GPU and cores were throttled (after the first 364 files), the rate of export was 41% faster with the fans on.

     

    * * *

     

    I don't think this is under the direct control of LR (or any typical app). It's the operating system and firmware that decide when to throttle.

     

    * * *

     

    I didn't think there were thermal issues with the Apple Silicon Macbook Pros. The last years of the Intel Macbook Pros were notorious for their bad thermal engineering, with throttled CPUs due to overheating and fans that got easily  clogged.

     

    It may be that the Apple designers have deliberately chosen to run the fans less aggressively in order to keep the Macbooks quieter. Many people really don't like to hear the fans running (like my wife).

     

     

     

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