Subject: 'sort' wastes cpu-cycles of all available cpus
From: "Schwidom, Frank" <[email-masked]>
To: "[email-masked]" <[email-masked]>
Date: Fri, 26 Oct 2012 09:12:40 +0200
List-Id: <debbugs-submit.debbugs.gnu.org>

In some situations sort wastes cpu-cycles of all available cpus.

Hi,

I refer to 'sort' of the following Version:

$ sort --version
sort (GNU coreutils) 8.7
Packaged by Gentoo (8.7 (p1))
Copyright (C) 2010 Free Software Foundation, Inc.
License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it.
There is NO WARRANTY, to the extent permitted by law.

Written by Mike Haertel and Paul Eggert.

on the system:

$ uname -a
Linux CUDA 2.6.38-gentoo-r6 #12 SMP Fri Sep 14 12:59:07 CEST 2012 x86_64 Intel(R) Xeon(R) CPU E5645 @ 2.40GHz GenuineIntel GNU/Linux

The problem causes, if the input of sort is very long but the output is not taken.

if i call:

# seq 1 10000000 | sort -R | wc -l
10000000

then sort itself uses only circa 10 cpus:

top:
 8316 root      20   0  359m 185m  676 S 1009  1.5   4:08.18 sort

or ca. 4 cpus in this case:

# seq 1 10000000 | sort -n | wc -l
10000000

top:
 8782 root      20   0  295m 185m  672 S  382  1.5   0:25.18 sort

while sort is running, this behaviour is ok. it would be ok too, if
it would use all cpus.

but, if i use:

# seq 1 1000000 | sort -n | less

and while im not scrolling to the bottom in 'less'
sort uses all cpus

top:
 9421 root      20   0  447m 109m  660 R 2295  0.9   3:12.72 sort

in this case, sort is already done sorting (it took and sorted
the whole input and 'less' displays values).
but it takes a lot of cpu-cycles on all cpus.

if i scroll to the bottom, 'less' takes all values of the sort output
and sort will end; this is ok.

Regards

Mit freundlichen Grüßen

Frank Schwidom
Dipl.-Inf. (FH)

Hochschule Lausitz (FH)
Fertigungstechnik/ Tribologie
Prof. Dr.-Ing. R. Winkelmann
Großenhainer Str. 57
01968 Senftenberg

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