LDP
/
man-pages
mirror of https://github.com/mkerrisk/man-pages
0
1
Fork 0
Code Releases Activity

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>
This commit is contained in:
Michael Kerrisk 2016-11-25 15:54:20 +01:00
parent c11d067046
commit 626dca367b
1 changed files with 19 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

22
man7/sched.7
View File

@ -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