P: High CPU usage makes it unusable during export

A percentage would likely be useful for the most people though I would prefer an absolute number. As I'm not having a problem with Export making my system unusable, perhaps my vote shouldn't count. 
 
While I've not done a scientific study of those who are having problems, they seem to be isolated to Mac users on relatively lightweight systems: all MacBooks and iMacs are lightweight hardware regardless of the Pro label. Windows and Mac Pro users seem to be unaffected though I would expect the problem to be just as serious on a Windows laptop even though Windows is somewhat more efficient at multi-tasking. 

Without overcomplicating the solution, a thread limitation should be based on the total number of available threads in the system.

"It looks like there are two camps, one that wants Lightroom exports to be super fast and don't care about any slow down."

...and Adobe has said it was their intention that LR support the second camp.  I don't recall any statements from Adobe saying they would add an option to LR to support the first (but then they rarely indicate ahead of time their intentions with respect to feature requests). 

Priorities are difficult to set in Unix (MacOS) and Windows (less so than Unix but still not easy) due to the architecture of the operating systems. It can be done but is likely to cause problems with other processes. 
 
Hence the solution normally implemented for a multi-threaded process like Export and Import is to provide a preference for the number of threads that can be utilized by the process. Not ideal, priorities would be a better solution but not until we get an OS with a new internal architecture. MS is working on one that we should see in a couple years. Apple is gradually moving off MacOS to iOS (and variants) for all their products. 
 
In the interim, it "should be" (no guarantees) relatively straightforward to deliver a Preference, MaxThreads=nn. Ideally it could be in the Export dialog so that it could be varied based on other tasks in process. 
 

It looks like there are two camps, one that wants Lightroom exports to be super fast and don't care about any slow down. The other camp wants to be able to use Lightroom while exporting and don't mind a slower export.

Seems to me Adobe needs to look at some sort of cpu utilization setting in preferences that can be adjusted by individual users.

Fully agree. 

John,  I would characterize this situation as an Issue for users.  I read through some of the comments in that statement you referenced above, and it's clear that people have strong feelings about this situation, but there is real disagreement about if/how to change the current export situation.

I think for most users, they won't care if the issue is called a Problem or Idea.  They just want to get their issue addressed.  That said, the way that software teams work, there might be separate resource allocations between Problems and Ideas.  That also said, Adobe needs to recognize that regardless of what this issue is, it should be a high priority to fix this issue in a way that satisfies most/all people. 

The solution is really not that difficult.  It's just a question of priorities.

Phil Burton

There have been a few statements by Adobe employees over the past several years that, after Export was changed in LR 6 / CC 2015 to use multiple cores more effectively, they intended that Export would not consume all of the available CPU, which would allow for interactive use.  I found one of those statements here:
https://feedback.photoshop.com/photoshop_family/topics/lr-cc-2015-2-and-up-cpu-usage-on-export-on-25...

Adobe categorizes a post here as a Problem ("bug" in the vernacular) if LR is not behaving as the developers intended.  It's categorized as an Idea ("feature request") if the current behavior was intended by the developers.

So when LR uses 100% CPU during export, making interactive use very difficult, that's a Problem.

Export performance test on:

• HP Z440 
• Xeon 6-core, 3.6/4 GHz
• 64GB RAM 
• from SSD on a PCIe adapter on the PCIe Bus, Samsung EVO 2TB 
• to SSD on a SATA SSD, Samsung EVO 1TB 
• Quadro K1200 
• 4K monitor

3 tests, exporting 100 raw images to jpeg at 100% quality, 4K resolution, sharpen for screen:

1. 2 min 54.4 sec - edited images 
2. 1 min 33.2 sec - unedited images 
3. 2-3X slowdown for editing concurrent with exporting another 100 unedited images, depending on the task. Library affected more than Develop, occasional flash of the develop window. 

 BTW, it is not a bug when something doesn't work the way we would prefer. 
 

On most computers, LR is good at limiting its total CPU usage during exports to about 85%, but on some computers, particularly those with a larger number of cores, LR uses close to 100%.  

This performance bug has been around for several years, and it should definitely be fixed. But if you need to get work done while waiting for Adobe to fix it, on Windows you can easily limit LR to use, say, 12 of 16 virtual processors:
https://feedback.photoshop.com/photoshop_family/topics/classic-cc-uses-90-cpu-during-export?topic-re...