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Bug 352807 - misbehaves with Linux' CPU hotplug/unplug
misbehaves with Linux' CPU hotplug/unplug
Product: libgtop
Classification: Core
Component: linux
Other All
: Normal normal
: ---
Assigned To: libgtop maintainers
libgtop maintainers
: 732305 (view as bug list)
Depends on:
Reported: 2006-08-25 08:41 UTC by Tomasz Torcz
Modified: 2018-01-10 19:45 UTC
See Also:
GNOME target: ---
GNOME version: ---

Description Tomasz Torcz 2006-08-25 08:41:58 UTC
Please describe the problem:
GNOME System Monitor is totally unaware of CPU Hotplug/Hotremove events.
It also have problem with "sparse" cpu numbers.

Steps to reproduce:
Scenario A:
1. Run System Monitor
2. Unplug CPU (echo 0 > /sys/devices/system/cpu/cpu1/online)

Scenario B:
1. Unplug CPU
2. Run System Monitor
3. Plug CPU (echo 1 > /sys/devices/system/cpu/cpu1/online)

Scenario C:
1. Run System Monitor on 4-way SMP system.
2. Unplug second or third CPU

Actual results:
Scenario A:
Unplugged CPU's line goes flat, but CPU is still displayed

Scenario B:
Freshly plugged-in CPU do not appear in monitor.

Scenario C:
SERIOUS! System Monitor shows only one (if second CPU was unplugged) or
two (if third CPU) CPU's graphs. It doesn't show fourth (and third) CPU's graph.

Expected results:
Scenario A:
Unplugged CPU's label should be grayed-out and percent display should be changed to "offline".

Scenario B:
Freshly plugged CPU should either:
a) appear
b) be un-grayed-out (see Scenario A expected action)

Scenario C:
CPUs 3 and 4 should be shown even if CPU2 is disabled. System Monitor shouldn't stop enumerating CPUs on first offline one.

Does this happen every time?

Other information:
Multicore laptops are becoming standard, and power management policy could turn off (unplug) unused CPUs. So this is rather imporant drawback in GNOME System Monitor.
Comment 1 M.Hotzen 2010-02-26 14:07:24 UTC
I can confirm this bug. I've got it with Version 2.28.0-0ubuntu1 on an Intel E5520 and with Version 2.16.0 (CentOS 5.4) on a Tyan VX50. I wonder why it was not fixed although it is known for a long time and pretty sticky over a lot of versions.
Comment 2 Robert Roth 2012-07-22 19:14:06 UTC
I can still reproduce this on Gnome System Monitor git HEAD.
Also see downstream report for ubuntu:
Comment 3 Robert Roth 2012-07-22 19:31:57 UTC
Reassigning this to libgtop, the library getting us the CPU information, as it determines the number of CPUs the following way [1]: starts reading /proc/stat line by line, increases a counter with each line, and checks if the line starts with cpu%d, counter. In case e.g cpu2 is offline, /proc/stat only has cpu0, cpu1, cpu3 on a quad-core, but as line 3 doesn't start with cpu2, but starts with cpu3, it stops counting the number of cores and tells system monitor that there are only 2 cores, cpu0 and cpu1. 

Comment 4 Robert Roth 2014-06-27 01:22:59 UTC
*** Bug 732305 has been marked as a duplicate of this bug. ***
Comment 5 GNOME Infrastructure Team 2018-01-10 19:45:01 UTC
-- GitLab Migration Automatic Message --

This bug has been migrated to GNOME's GitLab instance and has been closed from further activity.

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