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== Waiting, states, calculations ==
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Optimum load average should be the same as the number of processors (or in case of hyperthreading, virtual processors). ie not 2 for a dual processor sysem, 4 for a dual processor with hyper etc...
<small><span class="autosigned">—Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[User:Mchicago|Mchicago]] ([[User talk:Mchicago|talk]] • [[Special:Contributions/Mchicago|contribs]]) 19:08, 27 February 2006</span></small><!-- Template:Unsigned -->
A clearer, more detailed, and authoritative explanation of waiting, states, and calculation (including analysis of the operating system code) can be found in the reference listed under External Links (http://www.teamquest.com/resources/gunther/display/5/index.htm). Anyone contemplating changes to this section (I lack the necessary detailed knowledge) should take a close look at that reference.
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Confusion here seems to stem from the fact that Linux calculates load average differently from most UNIX systems: on most systems, only running or runnable threads count towards the load, but Linux also includes threads in certain types of sleeps (i.e., disk I/O). This difference becomes most significant during storage system stalls, such as NFS server failure, where the load average on Linux will spike because many threads will be blocked in NFS I/O indefinitely. I've updated the article a bit to reflect this distinction, but no of no other UNIX system that takes this approach.
It is my firmly held belief that most Unix systems (any that I've come across, certainly) behave in the way which
is described to be specific to Linux, in that processes in short-term wait, such as waiting for disk I/O to complete,
will contribute to the calculated load on the machine. This is certainly true for NetBSD, almost certainly true for
all the relatives (the other BSD flavors) given the common heritage. I'm also pretty sure that both Solaris and
HP-UX also behave in this manner, i.e. include processes in short-term uninterruptible wait as contributing to the
load on the machine. <span style="font-size: smaller;" class="autosigned">—Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[Special:Contributions/158.38.62.77|158.38.62.77]] ([[User talk:158.38.62.77|talk]]) 11:15, 26 November 2009 (UTC)</span><!-- Template:UnsignedIP --> <!--Autosigned by SineBot-->
[[Special:Contributions/212.59.34.129|212.59.34.129]] ([[User talk:212.59.34.129|talk]]) 08:37, 19 November 2009 (UTC) Harald
I'd like to know, how multi-core CPUs fit into the following sentence:
In a system with four CPUs, a load average of 3.73 would indicate that there were, on average, 3.73 processes ready to run, and each one could be scheduled into a CPU.
I'd assume, that a Dual CPU, Dual Core system counts for 4 parallel processes.
== Instantaneous percentage of CPU utilization on Windows?!? ==
The author states that "On Microsoft Windows PC systems, the system load is given as an instantaneous percentage of CPU utilization." That's not possible, there is no CPU "speedometer" on any processor chip set that I know of. An operating system can only recognize two basic states: idle (0% utilization) or not idle (100% utilization). To report a utilization between 0% and 100% requires that it average the two basic states over some time period. Most operating systems do this by sampling the current state during each clock interrupt and incrementing one of the two state counters (most operating systems also have sub-counters under Not Idle such as Wait I/O in UNIX or processing nested interrupts). The utilization that is then reported is the difference between the counters over some sampling interval divided by the total samples during the interval and that is what is reported as utilization. As for what time interval Windows utilities such as perfmon and the Logs & Alerts Service use I have no clue.
* Some chips scale frequency now, but your point is still 99% correct. [[User:128.135.99.80|128.135.99.80]] 19:57, 7 September 2006 (UTC)
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It's like measuring speed from an erratically moving car.
If that is to be fixed, it would have to somehow poll the frequency that the cpu is running at.
<small><span class="autosigned">—Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[User:70.54.202.152|70.54.202.152]] ([[User talk:70.54.202.152|talk]] • [[Special:Contributions/70.54.202.152|contribs]]) 13:03, 1 November 2006</span></small><!-- Template:Unsigned -->
:I suspect part of the problem is that the term "load average" is very well defined, but the term "load" is vague at best. This article is currently mostly about the Unix load average, and ''not'' about "Load (computing)". Whether we should change this article to be more general, or simply rename it to [[Load average]] and create a new [[Load (computing)]] stub with the rest of the content, I dunno. --[[User:DragonHawk|DragonHawk]] 02:06, 4 January 2007 (UTC)
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== Processes or jobs? ==
The article talks about "each process that is using CPU". I think it's more common to talk about "each job", which isn't necessarily synonymous. For example, a process with two threads can count as two jobs.
:I think the problem is that each UNIXoid operating system will use different terms. For example, on Linux your jobs are called "tasks".
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it referred to a batch file containing some non-interactive stuff to be done in a certain sequence (series or parallel or both).
A job usually contains more processes and has nothing to do with the load average we are talking about here.
<small><span class="autosigned">—Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[User:70.54.202.152|70.54.202.152]] ([[User talk:70.54.202.152|talk]] • [[Special:Contributions/70.54.202.152|contribs]]) 13:07, 1 November 2006</span></small><!-- Template:Unsigned -->
For unix, there are specific meanings to the terms "job" and "process". A job is in the jobtable, a process is in the process table. See `jobs` for a list of jobs for the current terminal, and `ps` for a list of process for the current system. Don't be confused by cron terminology; jobs aren't processes. --[[Special:Contributions/87.194.236.208|87.194.236.208]] ([[User talk:87.194.236.208|talk]]) 15:20, 4 May 2008 (UTC)
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I also remember seeing the Load Average used on TOPS20 before seeing it on BSD Unix.
-HWM <small><span class="autosigned">—Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[User:TenexHacker|TenexHacker]] ([[User talk:TenexHacker|talk]] • [[Special:Contributions/TenexHacker|contribs]]) 03:38, 3 September 2006</span></small><!-- Template:Unsigned -->
== Error in example of load average? ==
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To me, a load of 2.00 would mean that it's '''over'''loaded by 100%, not 200%.
<small><span class="autosigned">—Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[User:Vmardian|Vmardian]] ([[User talk:Vmardian|talk]] • [[Special:Contributions/Vmardian|contribs]]) 13:25, 21 November 2006</span></small><!-- Template:Unsigned -->
:The author did OK until they said "For example a load average of "3.73 7.98 0.50" on a single CPU system can be interpreted as:
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:This is NOT correct. (which is why I deleted that section previously, but it re-appeared).
::Yes, completely totally wrong. Wrong wrong wrong wrong. That is not what load average means at all. [[Special:Contributions/96.42.113.114|96.42.113.114]] ([[User talk:96.42.113.114|talk]]) 20:32, 21 August 2012 (UTC)
:As the author correctly stated earlier, load is how many processes is waiting to run (+ 1 actually running) on the system. e.g if there are 9 waiting and 1 running the load will be 10.
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:::In other words, it's possible to have a Load Average below 1.0 and have 100% CPU usage (single process using all CPU with no other processes waiting) but it's not possible to have a Load Average above 1.0 with less than 100% CPU usage (doesn't make sense to have lots of processes blocked with idle CPU). At least, that's how I read this. <small>—Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[Special:Contributions/66.92.218.124|66.92.218.124]] ([[User talk:66.92.218.124|talk]]) 20:21, 18 October 2007 (UTC)</small><!-- Template:UnsignedIP --> <!--Autosigned by SineBot-->
::::Wrong. So very wrong. Processes waiting on IO, thus are using ZERO CPU time, add to the load average. Thus it is entirely possible to have a high load average with less than 100% CPU usage. This is an indication that you are IO bound, NOT CPU bound. This is why just blindly upgrading your CPU because load average is high, is the wrong thing to do. This is why load average is meaningless on its own, and mostly meaningless even with other context. It tell you nothing you can't more easily figure out just looking at CPU usage in top and the blinking lights of your hard drive. [[Special:Contributions/96.42.113.114|96.42.113.114]] ([[User talk:96.42.113.114|talk]]) 20:32, 21 August 2012 (UTC)
:: seems to give a much clearer idea of the concept of load and load average. i quote an important point:
"It is important to remember that a CPU is a discrete state machine. It really can be at only 100%, executing an instruction, or at 0%, waiting for something to do. There is no such thing as using 45% of a CPU. The CPU percentage is a function of time."
[[User:Hackeye|Hackeye]] ([[User talk:Hackeye|talk]]) 05:03, 24 November 2007 (UTC) hackeye
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This page needs to decide if it is about unix (& clones) load averages, or about the concept of computer load. There isn't currently a page about unix load averages, and most of the unix related stuff here is reasonable enough to start one. The windows section needs to be expanded or explained. The "Other Meanings" section would probably be better shifted to their respective pages, or made into separate stub pages. --[[User:CalPaterson|CalPaterson]] ([[User talk:CalPaterson|talk]]) 15:29, 4 May 2008 (UTC)
:The windows section needs deleted, really. Windows has no use for load averages. [[Special:Contributions/89.240.240.107|89.240.240.107]] ([[User talk:89.240.240.107|talk]]) 13:19, 12 May 2008 (UTC)
== "Load average is not CPU utilization" Section ==
I just removed a section titled "Load average is not CPU utilization" added by [[User:Sp0|Sp0]] a few months ago. The text of the section was:
: Even though the statements in the previous section might suggest that load average is related to CPU utilization because the section relates CPU to load average, load average does not measure CPU utilization of processes. One reason it does not do this is because load averages computations of processes are in a wrong order to relate to trend information of CPU utilization. In other words, the calculations and numbers directly produced by load averages do not compute numbers in an order from more CPU intensive to less CPU intensive or vice versa, nor do they give computations of numbers that would give another way that would result in direct information about CPU utilization. In summary, the functions of load average give numbers based on load queue of processes. The next section uses the same reference to suggest that load average is not very important or vital to system performance information until or unless the a system's CPU is heavily loaded to around 100%. Then, at levels close to 100%, load average could be very important or significant to determinacy of system performance; however, this would be because average load numbers give direct information about process queue length not CPU utilization -- which is something they do not give direct information about.
Without making any comment on the accuracy of this information, there are two severe problems with this: First, it is almost completely incomprehensible due to grammatical errors and a generally rambling style. Second, the section existed to contradict the rest of the article. Sp0, if you believe the article is factually inaccurate, the correct response is to edit or replace the existing text to make it accurate, and preferably also to include citations of reliable sources to prevent an edit war. -- [[User:Tyler McHenry|Tyler]] ([[User talk:Tyler McHenry|talk]]) 18:24, 8 January 2010 (UTC)
== Misleading and wrong... ==
This article has so many sections that are misleading or wrong that I don't even know where to start... Almost want to delete much of it, yet lazy to rewrite...
# Adding to the note by previous user, "Load average is not CPU utilization" is correct. Load average is not necessarily CPU utilization. If the system was hanging on disk all the time, and CPU was hitting high iowait, it's not exactly "utilizing" the CPU.
# Statements like this is just wrong: "(no processes had to wait for a turn)". We already know processes waited on the minute average, just because we change averages doesn't magically change history. Average does not define minimums and maximums.
# To use the word "overloaded" and "underloaded" is correct but also highly misleading. Your system may not be conceptually underloaded at all even if the system has under 1.00 load average. Loads spike and drop, once again, average does not define minimums and maximums. Whether it's underloaded or not depends on what is running and how it's affecting the system. To give a specific example, let's say we have a voice communication program and every time you say something, it uses more CPU. But your CPU can't handle the increased load and thus sends stuttering messages. So, the communication program overloads your CPU. But you don't talk 100% of the time, so, it may be underloaded most of the time. Then to say your CPU is underloaded but your CPU couldn't handle the communication program is highly confusing.
# "This means that this CPU could have handled all of the work scheduled for the last minute if it were 1.73 times as fast" is also untrue. Load average, once again, is not purely dependent on CPU. That implies that load average only depends on CPU.
--[[User:Grumpyland|-Grumps]] ([[User talk:Grumpyland|talk]]) 06:50, 15 October 2012 (UTC)
== Confusion on Hz definition ==
"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. (Hz variable is the pulse rate of particular Linux kernel activity. 1Hz is equal to one clock tick; 10ms by default.) Although the Hz value can be configured in some versions of the kernel, it is normally set to 100. The calculation code uses the Hz value to determine the CPU Load calculation frequency. Specifically, the timer.c::calc_load() function will run the algorithm every 5 * Hz, or roughly every five seconds. Following is that function in its entirety:"
The above paragraph in the article is very confusing.
I think it is confusing Hz with the Linux kernel interrupt timer.
>> 1Hz is equal to one clock tick; 10ms by default.
If the definition of hertz is "cycles per second" as defined by the Hertz article on Wikipedia, then how can 1 Hz be 10ms?
1 Hz would be 1 cycle per second, which would mean that the clock ticks once per second.
I think the 10ms is actually referring to the Linux kernel interrupt timer which is normally set to 100, or roughly every 10 ms.
The kernel interrupt will fire 100 times a second.
>> Although the Hz value can be configured in some versions of the kernel, it is normally set to 100.
Huh? I thought it just said that 1 Hz is equal to one clock tick?
I guess that what it is referring to is the Linux timer interrupt frequency again.
>> Specifically, the timer.c::calc_load() function will run the algorithm every 5 * Hz, or roughly every five seconds.
That makes sense if the Hz value is 1 (one cycle per second). <span style="font-size: smaller;" class="autosigned">— Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[Special:Contributions/69.84.133.248|69.84.133.248]] ([[User talk:69.84.133.248|talk]]) 15:24, 25 April 2013 (UTC)</span><!-- Template:Unsigned IP --> <!--Autosigned by SineBot-->
== Notes ==
There is currently one note regarding an error in a paper. This should probably be signaled to the
author of that paper instead of sitting on a wiki page. What's also missing is some reasoning behind
the error that was signaled.
Would be nice if the wiki page would recommend a correct reference for a complete description of the
concept.~~ <small class="autosigned">— Preceding [[Wikipedia:Signatures|unsigned]] comment added by [[Special:Contributions/86.124.79.201|86.124.79.201]] ([[User talk:86.124.79.201|talk]]) 07:26, 14 March 2015 (UTC)</small><!-- Template:Unsigned IP --> <!--Autosigned by SineBot-->
There is no error.
[[Special:Contributions/194.166.103.157|194.166.103.157]] ([[User talk:194.166.103.157|talk]]) 21:41, 17 March 2015 (UTC)
== definition is ridiculous ==
The term "system load" (the title of this article) cannot be defined using the term itself.
: In UNIX computing, the system load is a measure of the amount of computational work that a computer system performs. The load averagerepresents the average system load over a period of time. It conventionally appears in the form of three numbers which represent the system load during the last one-, five-, and fifteen-minute periods.
This is an unacceptable definition.
I am capable of providing a substantial rewrite to this article and creating one that is much more useful in explaining how this works on Unix systems (and probably the article should be retitled as 'system load' is a dramatically different term on Unix (&Unix-like) systems than it is on mainframe and Windows systems (as well as realtime systems like embedded). I note also that this article has "needed references" since 2010.
As somebody who has been an editor of this fine encyclopedia since 2004, I am hesitant to even bother making these changes as I am aware the piranhas will attack and say "well you cannot just go and edit this thing without sources." I have been a Unix engineer for twenty years and ''I am a source''. You are unlikely to find sources to corroborate things in this article as Unix is a moving target. As kernels in Linux have progressed from 2.2 to 2.4 to 2.6 and the 3 kernels, system load has changed dramatically and how we measure it has changed.
I therefore also feel that the tag demanding this article be better referenced is preposterous. The tag should be removed, and people who have their dander up about sources on this article should perhaps be asked to undander themselves. <b>... </b><span style="background-color: #11cbc4;width:52px;height:16px;font-size:12px;p{text-align:center}">[[user:avriette|jane avriette]]:[[user_talk:avriette|talk]]</span> 19:15, 28 October 2015 (UTC)
:I am retired editor but i have made a pledge to provide requests for comments when asked. Unfortunately the point about references can not be by passed however the definition of references of taggers is generally they do not understand each topic and think that we need 1000 references, but the Wikipedia policy on reference does not say we need lot but for anything written it must be backed up by a reliable third party source. You are quite entitle to rewrite it using your knowledge but you would need to provide a reference that backs up what your saying in this day and age finding reference is not as hard as it was 10 years ago granted this topic will have less references than say a well published subject but there is references. My suggestion is to make a sub test page of the article and then write up your changes how you think the page should be and then request for comment on that as long as it complies with principle standards of Wikipedia then it can not be objected you will find there is some editors who will quote obscure policies to block you but these policies are all derived from the core policies which i can quote later if there is issues. Good luck on the rewrite as it does need a rewrite as with a lot of other articles also if you think the subject matter ie the title is not write then suggest a new one and we can have it moved if supported[[User:Andrewcrawford|<span style="color:LightBlue;">Andrewcrawford</span>]] ([[User talk:Andrewcrawford|<small>talk</small>]] - [[Special:Contributions/Andrewcrawford|<small>contrib</small>]]) 17:24, 29 October 2015 (UTC)
::these "obscure policies" are why i stopped editing. <b>... </b><span style="background-color: #11cbc4;width:52px;height:16px;font-size:12px;p{text-align:center}">[[user:avriette|jane avriette]]:[[user_talk:avriette|talk]]</span> 20:18, 18 November 2015 (UTC)
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