3 ms·

htop is an excellent tool. I appreciate his valiant effort to explain what load average is; it's confused Unix users forever. His explanation is more or less ri

htop is an excellent tool. I appreciate his valiant effort to explain what load average is; it's confused Unix users forever. His explanation is more or less right but I think misses a bit of context about the old days of Unix performance. It used to be in the early 90s that Unix systems were quite frequently I/O bound; disks were slow and typically bottlenecked through one bus and lots of processes wanted disk access all the time. Swapping was also way more common. Load average is more or less a quick count of all processes that are either waiting on CPU or waiting on I/O. Either was likely in an old Unix system, so adding them all up was sensible. In modern systems your workload is probably very specifically disk bound, or CPU bound, or network bound. It's much better to actually look at all three kinds of load separately. htop is a great tool for doing that! but the summary load average number is not so useful anymore.

codetrotter 7y ago
> In modern systems your workload is probably very specifically disk bound, or CPU bound, or network bound. It's much better to actually look at all three kinds of load separately. Linux recently got an interface called Pressure Stall Information that lets you collect accurate measures of CPU, I/O and memory pressure. https://www.kernel.org/doc/html/latest/accounting/psi.html https://www.kernel.org/doc/html/latest/accounting/psi.html
- bluetech 7y ago
  PSI is a perfect fit for htop. I sent a PR to add it some time ago (https://github.com/hishamhm/htop/pull/890 https://github.com/hishamhm/htop/pull/890) but it hasn't been merged yet.
- usr1106 7y ago
  Kernel 4.20, so probably not yet available on many production systems.
exikyut 7y ago
Comparison: - Horribly under-specced machine (8GB RAM) with way too many (~150) tabs open -> continuous swap stalls that last for minutes at a time and freeze the mouse cursor: 5-second load average of 12-20 - 6-year old Android phone doing tasks in the background, generally feeling more than adequately performant, and lukewarm enough that you aren't sure if it's your hand or the phone generating the warmth: load average of 12-13 - Building Linux with -j64 to see what would happen: 5-second load average of 0.97... 0.99... 49.40... 127.21... ^C^C^C^C^C^C^C^C^C 180.66... ^C^C^C^C^C^CCCCCCC^^^CCcccCCcCC 251.22... ^C^C^C^C^C^C ^C^C^C^C ^C^C^C ^C^C^C^C^C^C ^^^CCCCC^C^C^C (mouse finally moves a few pixels, terminal notices first ^C) 245.55... 220.00... 205.42... 198.94... - Resuming from hibernation with 20GB of data already in swap: 0.21... 0.15... 0.10... 251.50... 280.12... 301.69... 362.22... 389.91... 402.40... 308.56... 297.21... 260.66... 254.99... (etc; this one takes a while)

codetrotter 7y ago

> In modern systems your workload is probably very specifically disk bound, or CPU bound, or network bound. It's much better to actually look at all three kinds of load separately. Linux recently got an interface called Pressure Stall Information that lets you collect accurate measures of CPU, I/O and memory pressure. https://www.kernel.org/doc/html/latest/accounting/psi.html https://www.kernel.org/doc/html/latest/accounting/psi.html

bluetech 7y ago
PSI is a perfect fit for htop. I sent a PR to add it some time ago (https://github.com/hishamhm/htop/pull/890 https://github.com/hishamhm/htop/pull/890) but it hasn't been merged yet.
usr1106 7y ago
Kernel 4.20, so probably not yet available on many production systems.

exikyut 7y ago

Comparison: - Horribly under-specced machine (8GB RAM) with way too many (~150) tabs open -> continuous swap stalls that last for minutes at a time and freeze the mouse cursor: 5-second load average of 12-20 - 6-year old Android phone doing tasks in the background, generally feeling more than adequately performant, and lukewarm enough that you aren't sure if it's your hand or the phone generating the warmth: load average of 12-13 - Building Linux with -j64 to see what would happen: 5-second load average of 0.97... 0.99... 49.40... 127.21... ^C^C^C^C^C^C^C^C^C 180.66... ^C^C^C^C^C^CCCCCCC^^^CCcccCCcCC 251.22... ^C^C^C^C^C^C ^C^C^C^C ^C^C^C ^C^C^C^C^C^C ^^^CCCCC^C^C^C (mouse finally moves a few pixels, terminal notices first ^C) 245.55... 220.00... 205.42... 198.94... - Resuming from hibernation with 20GB of data already in swap: 0.21... 0.15... 0.10... 251.50... 280.12... 301.69... 362.22... 389.91... 402.40... 308.56... 297.21... 260.66... 254.99... (etc; this one takes a while)