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I have two identical Linux laptops (Core™ i7-4810MQ with 32GB RAM) both running Ubuntu 16.04. Running seemingly any command on machine 2 takes about 4-12 times as long as on machine 1, depending on the activity. This was noticed late last week while running some simple gradle builds and hasn't changed since then.

To measure, I ran a C++ build on each system. I chose this one because I make the C++ program a few months ago and had built it on both systems. They weren't measured, but they took roughly the same amount of time back then. Running the follow on each system today:

make clean && time make -j8

System 1 finishes with the following report:

real    0m54.627s
user    5m54.188s
sys     0m23.008s

System 2 takes much longer:

real    11m1.053s
user    65m59.512s
sys     4m10.404s

Searches on Stack Exchange and Google lead to numerous threads on diagnosing the issue, but they all seem to assume that there is a process slowing the machine down. top, iostat and gnome-system-monitor etc report identical resource usage on both machines - neither is busy doing anything difficult and there is lots of CPU, memory, bandwidth and io available.

What are the first things to check when a Linux system is clearly under-performing, but it's not a hardware capability limitation?

chadsgilbert
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  • Powersaving options in your OS and / or BIOS? Memory errors? Disk errors? Maybe also try to use http://collectl.sourceforge.net/ (or similar) to measure performance. – Lenniey Mar 12 '18 at 17:29
  • Good suggestions, thanks! We started looking into some power settings, but stumbled blindly onto the true issue - `gradle` runs a daemon. That was, for reasons still unknown to us, slowing the entire machine down. Still unclear to me why that wouldn't have shown up in any of the monitoring tools I'm aware of, but I'm excited to have this worked out. – chadsgilbert Mar 12 '18 at 18:29

1 Answers1

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I won't accept this answer, but here's the lesson I've learned: if the analysis tools can't help, think through what's changed recently on the system. The only change we had made to System 2 that hadn't also been made on System 1 in the past week, was to start the Gradle daemon on System 2. That had to be the cause of the problem, and so it was.

chadsgilbert
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