photo editing - hardware priority 5K imac

Discussion in 'iMac' started by MP3.1, Oct 18, 2015.

  1. MP3.1 macrumors newbie

    Joined:
    Mar 23, 2013
    #1
    Hi all,

    I'm looking to upgrade to a 5K imac very soon (up from 2008 Mac Pro :p) and would like your advice on which of the following should have priority (in what order) if my main usage for the imac is photo editing (big files on CS and Lightroom):

    1. CPU
    2. RAM (will buy the 8Gb, upgrade to (likely) 24Gb from 3rd party).
    3. Storage (which will be SSD only 512Gb)
    4. GPU

    Will go for the top model but am doubting whether or not to invest in either a GPU or CPU bump, or perhaps even 24=>32Gb RAM.

    Thanks a lot!
     
  2. ixxx69 macrumors 6502a

    Joined:
    Jul 31, 2009
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    United States
    #2
    Sounds good... should serve you well.

    The most likely thing you might need is a RAM upgrade, but unless you KNOW you need more than 8GB right now, I would suggest holding off on that... having more RAM than you need doesn't help much with performance.

    A GPU upgrade isn't going to be of great value for photo editing. Faster CPU is always a plus, but not really needed. If a little extra money won't be missed, certainly get the upgrades, but you shouldn't feel like you're missing out if you don't.
     
  3. AppleDroid macrumors 6502a

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    Apr 10, 2011
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    Illinois
    #3
    There's a thread on this topic you can check out here: http://forums.macrumors.com/threads/best-imac-configuration-for-photo-editing.1928711/
     
  4. Wahlstrm macrumors 6502a

    Wahlstrm

    Joined:
    Dec 4, 2013
    #4
    It´s easier to work with a slow CPU than insufficient amounts of RAM.
    Slow CPU = it takes a bit longer.
    Low on RAM = it takes for ever.. :)

    CPU upgrade is probably still more worth it than GPU for photography needs.
    That higher singel core performance will boost a lot of tasks, GPU will boost a few specific tasks.
     
  5. Textureboy macrumors 6502

    Textureboy

    Joined:
    Jul 25, 2012
    #5
    I always thought 16GB of RAM was overkill but after doing intensive photo editing with lots of layers I found that it wasn't enough. So definitely increase your RAM to your liking and needs. 16GB of RAM will be fine with regular lightroom editing.
     
  6. arbitrage macrumors 6502a

    Joined:
    Mar 19, 2009
    #6
    Our other thread was referenced above and there is now 2 pages of discussions about this....

    LR still depends most on single core CPU speed for generating previews which is the biggest time suck for me. I don't do much at all in PS anymore. LR's GPU use is still not that great although it does now have it.

    Personally, I've decided to go:

    4GHz i7
    8GB (will add 16GB aftermarket for 24GB)
    512 SSD
    Max GPU card with 4GB (mostly to future proof as much as possible in case Adobe starts to use the GPU more) also must help with driving that 5K display (although I guess the base GPUs can do it okay or Apple wouldn't offer them).
     
  7. joema2 macrumors 65816

    joema2

    Joined:
    Sep 3, 2013
    #7
    That is not what I've observed. I just imported and generated 1:1 previews for 42 megapixel raw images from a Sony A7RII. As you can see from the attached iStat Menus thread display, all physical cores are at high utilization for the entire process. This was on a top-spec 2013 iMac 27 on OS X 10.10.5.

    The thread dispatcher chose to schedule every other virtual CPU on the hyper threaded i7 vs all of them. That is probably to avoid cache thrashing. However preview generation on LR is heavily multi-threaded and will use all available physical cores. The more cores the faster it will run.
     

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  8. Wahlstrm macrumors 6502a

    Wahlstrm

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    Dec 4, 2013
    #8
    Lr never use more than 50% of my CPU..
    On my dual core it uses 2/4 virtual cores and on my quad core it uses 4/8 virtual cores.
    This is why higher Ghz is better than extra cores in most of Adobes programs.
     
  9. maflynn Moderator

    maflynn

    Staff Member

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    May 3, 2009
    Location:
    Boston
    #9
    Of the CPU choices will any of us really notice a difference between the lowest tier CPU in the 5k iMac and the highest?

    I think my order of priority would be
    Storage (because a slow drive will drag Lightroom down) An SSD is what I'm looking at.
    GPU - Lightroom now leverages the GPU more then it used too, so a nice GPU will be helpful.
    CPU
     
  10. joema2 macrumors 65816

    joema2

    Joined:
    Sep 3, 2013
    #10
    No, it is using 100% of your available physical cores. In fact it is probably reporting 200% utilization on your Mac, not 50%. They count each core (whether physical or logical) as 100%.

    Using nearly 100% of each physical core on a two-core machine means LR is multi-threaded and is efficiently harnessing all available physical CPU cores. It does not depend "most on single core CPU" when generating previews.

    Whether OS X dispatches the thread pool across all logical cores on a hyperthreaded CPU has nothing to do with the app. That is an OS X decision. It can potentially hurt performance to use all hyperthreaded cores. This is due to cache thrashing.

    Given a pool of runnable threads, in some cases it is beneficial to dispatch these to all logical cores of a hyperthreaded CPU. In other cases it is better to dispatch to every other core (just the physical cores). The OS X thread dispatcher tries to make the best decision. This has nothing to do with whether the app is efficiently multi-threaded or not.
     
  11. Wahlstrm macrumors 6502a

    Wahlstrm

    Joined:
    Dec 4, 2013
    #11
    I have tried this on several mac´s over several years. Lr has never used more than 50% of the CPU.
    It uses 200% (of 400% MAX) on my dual core i7 and 400% (of 800% MAX) on my Quad Core i7.
    I also use DXO Optics Pro and that program use just shy of 800% when exporting photos.
     
  12. Alesc macrumors 6502

    Alesc

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    Nov 11, 2014
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    France
    #12
    What is your system? I see you are running the 780M AND the Iris Pro? I have the same late 2013 iMac, I can see the 780M in iStat Menu, but not the Iris Pro... How did you do?
     
  13. AppleDroid macrumors 6502a

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    Apr 10, 2011
    Location:
    Illinois
    #13
    LR can be finicky that's for certain. A trick I learned when batch exporting groups of photos is to do them in small sets. If I export all at once LR may only use half of the available HT Cores but if I break them into 4 separate exports it shoots up near 100% (or 800% depending how you read it) CPU usage.

    EDIT: I should have spelled it out take 100 images, select sets of 25 and export simultaneously rather than one large group.
     
  14. joema2 macrumors 65816

    joema2

    Joined:
    Sep 3, 2013
    #14
    That means it IS essentially using 100% of the CPU. The 800%, etc. numbers are a misleading artifact of how the CPU monitor reports hyperthreaded activity. This can be easily proven. You can measure the elapsed wall clock time to execute a job when DXO reports 800% utilization, then disable hyperthreading with the CPUSetter utility (likely safe, but use at your own risk): http://www.macupdate.com/app/mac/48580/cpusetter

    You will see CPU utilization drop to 400% but performance won't drop by nearly that much. IOW going from 400% to 800% does not remotely improve performance by that rate because hyperthreading cannot provide that degree of speedup. This is unrelated to Amdahl's law that limits multi-core speedup.

    When about 50% CPU utilization is reported on a multithreaded CPU-bound job on a hyperthreaded CPU, this often means the OS X thread dispatcher is giving you 100% of available resources that can be efficiently employed. This can be confirmed by inspecting the cores with iStat Menus or similar. If every other logical core is scheduled, that is the cause, not any deficiency of the application. If it were possible during that workload via thread affinity APIs to force it to use all logical cores, the reported CPU % would be higher but your elapsed wall clock execution time would be slower.

    Other applications (e.g. DXO) have characteristics which the OS X thread dispatcher judges to be advantageous to schedule on all logical CPUs, so in that case OS X does so. But it's not double the CPU capacity, rather the hyperthreaded logical cores simply fill in some pipeline wait states, and that is *reported* as double the CPU utilization. It is not.
     
  15. joema2 macrumors 65816

    joema2

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    Sep 3, 2013
    #15
    That is a good question. I think the i7-4771 in my iMac does not have Iris Pro but HD Graphics 4600. I have not done anything special to change this. It must be a bug in how iStat Menus reports the integrated graphics.

    I am running iStat Menus 4.22 (463) on OS X 10.10.5.

    I notice iStat Menus also reports Iris Pro Graphics on my 2015 MBP with i7-4980HQ, but that CPU does have Iris Pro Graphics 5200. I think it's a bug in iStat Menus, however I cannot explain why your similar iMac does show the same integrated GPU. If you are running a different version of iStat Menus or OS X, that might be the answer.
     
  16. Alesc macrumors 6502

    Alesc

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    France
    #16
    OS X 10.10.5 and iStat Menu 5.11, and I only see the 780M...
     
  17. joema2 macrumors 65816

    joema2

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    Sep 3, 2013
    #17
    I upgraded to 5.11 and I no longer see Iris Pro. As I suspected it was a bug in iStat Menus.
     
  18. Alesc macrumors 6502

    Alesc

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    #18
    OK, thanks a lot for your answer :)
     
  19. bhilibb macrumors newbie

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    Oct 16, 2015
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    Germany
    #19
    Now that I have my new iMac I can definitely prove that the priority must be as posted. I just managed to get about 100°C on all my i7 cores when using Lightroom and switching between large RAW files of a Canon 5DSR. The GPU was not that important. It mostly uses 3/4 of RAM of my M395. So I think I made the right decision in buying the i7 and the smaller GPU.
     
  20. Enrico macrumors 6502

    Enrico

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    Feb 6, 2007
    Location:
    Milano / Roma
    #20
    How much RAM are you guys using with Lightroom & RAW files?
    I ordered the base 8GB from Apple, and wondering whether going with 8GB or 16GB in the 2 empty slots.
     
  21. maflynn Moderator

    maflynn

    Staff Member

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    Boston
    #21
    I think 8GB is fine for LR, though if you have the funds it may not hurt to have the upgrade now, since its a bear to upgrade the iMac yourself.
     
  22. bhilibb macrumors newbie

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    Oct 16, 2015
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    Germany
    #22
    With the RAW files from the 5DSR I used about half of the 8GB RAM that I got.
     
  23. Enrico macrumors 6502

    Enrico

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    Feb 6, 2007
    Location:
    Milano / Roma
    #23
    Could it be because Lightroom is ilimiting itself to 50% of the total available RAM?
    If so, people with 16GB RAM, are they noticing 8GB of RAM used by Lightroom?
     
  24. bhilibb macrumors newbie

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    Oct 16, 2015
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    Germany
    #24
    Lightroom itself uses around 2gb at the moment. Applying some filters in Photoshop it needs 2.4gb.
     
  25. Enrico macrumors 6502

    Enrico

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    Feb 6, 2007
    Location:
    Milano / Roma
    #25
    Wow! LR is a much more conservative/efficient option compared to the old Aperture, at least RAM wise :)
    I remember seeing Aperture on my old MP using more than 10GB easily....
     

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