Load (computing): Difference between revisions

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== Reckoning CPU load ==

On Linux systems, the load-average is not calculated on each clock tick, but driven by a variable value that is based on the HZ frequency setting and tested on each clock tick. This setting defines the kernel clock tick rate in [[Hertzhertz]] (times per second), and it defaults to 100 for 10ms10 ms ticks. Kernel activities use this number of ticks to time themselves. Specifically, the timer.c::calc_load() function, which calculates the load average, runs every {{tt|1=LOAD_FREQ = (5*HZ+1)}} ticks, or about every five seconds:

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The "sampled" calculation of load averages is a somewhat common behavior; FreeBSD, too, only refreshes the value every five seconds. The interval is usually taken to not be exact so that they do not collect processes that are scheduled to fire at a certain moment.<ref>{{cite web |title=How is load average calculated on FreeBSD? |url=https://unix.stackexchange.com/a/342778 |website=Unix & Linux Stack Exchange}}</ref>

A post on the Linux mailing list considers its {{tt|+1}} tick insufficient to avoid Moire[[Moiré pattern|Moiré artifacts]] from such collection, and suggests an interval of 4.61 seconds instead.<ref>{{cite web |last1=Ripke |first1=Klaus |title=Linux-Kernel Archive: LOAD_FREQ (4*HZ+61) avoids loadavg Moire |url=https://lkml.iu.edu/hypermail/linux/kernel/1111.1/02446.html |website=lkml.iu.edu |date=2011}} [httphttps://ripke.com/loadavg/moire graph & patch<!-- Actual title at target: Moiré patterns in linux load average (Moiré mangled in title as Moiré) -->]</ref> This change is common among [[Android (operating system)|Android system]] kernels, although the exact expression used assumes an HZ of 100.<ref>{{cite web |title=Patch kernel with the 4.61s load thing · Issue #2109 · AOSC-Dev/aosc-os-abbs |url=https://github.com/AOSC-Dev/aosc-os-abbs/issues/2109 |website=GitHub |language=en}}</ref>

== Other system performance commands ==