diff options
| author | Michael Kerrisk <mtk.manpages@gmail.com> | 2016-11-25 15:54:20 +0100 |
|---|---|---|
| committer | Michael Kerrisk <mtk.manpages@gmail.com> | 2016-11-29 21:50:15 +0100 |
| commit | 626dca367b3183fe6737609c55bdbfe437cdd8cb (patch) | |
| tree | 1bfd0591d474a3247893733fc0c129aca64ead71 /man7/sched.7 | |
| parent | c11d067046a553ec08104699918510ad4e23d21f (diff) | |
| download | man-pages-626dca367b3183fe6737609c55bdbfe437cdd8cb.tar.gz | |
sched.7: Further clarify details of group scheduling
After comments by Mike Galbraith.
Reported-by: Mike Galbraith <efault@gmx.de>
Signed-off-by: Michael Kerrisk <mtk.manpages@gmail.com>
Diffstat (limited to 'man7/sched.7')
| -rw-r--r-- | man7/sched.7 | 22 |
1 files changed, 19 insertions, 3 deletions
diff --git a/man7/sched.7 b/man7/sched.7 index 99ad8065ff..d82813158c 100644 --- a/man7/sched.7 +++ b/man7/sched.7 @@ -717,7 +717,10 @@ distribution of CPU cycles across task groups. The benefits of this for interactive desktop performance can be described via the following example. -Suppose that there are two autogroups competing for the same CPU. +Suppose that there are two autogroups competing for the same CPU +(i.e., presume either a single CPU system or the use of +.BR taskset (1) +to confine all the processes to the same CPU on an SMP system). The first group contains ten CPU-bound processes from a kernel build started with .IR "make\ \-j10" . @@ -727,9 +730,22 @@ each receive half of the CPU cycles. That is, the video player will receive 50% of the CPU cycles, rather than just 9% of the cycles, which would likely lead to degraded video playback. -Or to put things another way: +The situation on an SMP system is more complex, +.\" Mike Galbraith, 25 Nov 2016: +.\" I'd say something more wishy-washy here, like cycles are +.\" distributed fairly across groups and leave it at that, as your +.\" detailed example is incorrect due to SMP fairness (which I don't +.\" like much because [very unlikely] worst case scenario +.\" renders a box sized group incapable of utilizing more that +.\" a single CPU total). For example, if a group of NR_CPUS +.\" size competes with a singleton, load balancing will try to give +.\" the singleton a full CPU of its very own. If groups intersect for +.\" whatever reason on say my quad lappy, distribution is 80/20 in +.\" favor of the singleton. +but the general effect is the same: +the scheduler distributes CPU cycles across task groups such that an autogroup that contains a large number of CPU-bound processes -does not end up overwhelming the CPU at the expense of the other +does not end up hoffing CPU cycles at the expense of the other jobs on the system. A process's autogroup (task group) membership can be viewed via the file |