4 ms·
This is great work in general and excellent historical research. As an additional historical note: in Unix, load averages were introduced in 3BSD, and at that
by siebenmann 9y ago
This is great work in general and excellent historical research.
As an additional historical note: in Unix, load averages were introduced in 3BSD, and at that time they included processes in disk IO wait and other theoretically short-term waits that weren't interruptible. This definition was carried through the BSD series and onward into Unixes derived from them, such as the initial versions of SunOS and Ultrix. At some point (perhaps SunOS 3 to SunOS 4, perhaps later), the SunOS/Solaris definition changed to be purely runable processes.
(I'm not sure what System V derived Unixes such as Irix, HP-UX, and so on did, and their kernel source is not readily available online for spelunking.)
As of early 2016 when I last looked at this, the situation on FreeBSD, OpenBSD, and NetBSD was somewhat tangled. FreeBSD load average only included runable processes, but NetBSD and OpenBSD counted some sleeping or waiting processes as well.
- brendangregg 9y agoThanks, I didn't know those Unix versions included disk I/O.
- cyphar 9y agoI think the reason for Sun changing it was due to the advent of NFS, which made measures of process based on I/O blocking inaccurate (and bound to network latency). I believe Cantrill mentioned this factoid at some point, but I don't recall the reference.
- thatcks 9y agoAs it happens, this isn't the case. Sun introduced NFS in SunOS 2, which unsurprisingly had the BSD view of load averages and did count NFS IO as short-term waits. A NFS server with problems could send client load averages up to monstrous levels (a load average of several hundred was not unusual, all of it from processes waiting for the NFS server) and many sysadmins got to see this first hand at the time.
- cyphar 9y agoMy point was that the reason for changing it is because of NFS and that it caused sysadmins to become confused. Not that it was changed along with the NFS release.
- EvanAnderson 9y agoWhen details of a piece of "open" software are so easily lost I shudder to think about the vast quantity of "closed" software that have had their history lost. I also kept thinking about how the term "software archaeology" (which I first saw in the 1999 Vernor Vinge novel "A Deepness In the Sky") becomes more and more mainstream each day.
- taneq 9y agoI always thought "programmer-at-arms" was a brilliant job title and well describes what some of us do.
- ams6110 9y agoThe numbers are definitely not comparable between Linux and some other unix variants. OpenBSD "idle" load average are about 1, for example.