Bug 434040 - Default combined CPU usage graph is less usable than averaged view
Summary: Default combined CPU usage graph is less usable than averaged view
Status: RESOLVED FIXED
Alias: None
Product: plasma-systemmonitor
Classification: Applications
Component: general (other bugs)
Version First Reported In: 5.21.2
Platform: Gentoo Packages Linux
: HI normal
Target Milestone: ---
Assignee: KSysGuard Developers
URL:
Keywords: usability
: 442509 463761 490895 501152 512366 (view as bug list)
Depends on:
Blocks:
 
Reported: 2021-03-06 02:37 UTC by Nicolas Werner
Modified: 2025-11-27 03:33 UTC (History)
9 users (show)

See Also:
Latest Commit:
Version Fixed/Implemented In: 6.4.0
Sentry Crash Report:


Attachments
Comparison of the old and new graphs with different settings and sizes (627.30 KB, image/png)
2021-03-06 02:37 UTC, Nicolas Werner
Details

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Description Nicolas Werner 2021-03-06 02:37:45 UTC
Created attachment 136423 [details]
Comparison of the old and new graphs with different settings and sizes

SUMMARY

There are multiple issues here. In the default size, the percentages below the CPU graph are unreadable. This should be partially fixed by https://invent.kde.org/frameworks/kquickcharts/-/merge_requests/28
But KSysguard solved that more nicely, by first shrinking the legend to just colored percentages. You should still wrap them at some point, because otherwise 48 threads will fit on pretty much no screen, but having a colored line next to it is not very useful at that size.

Secondly, the default of using a stacked chart leads to a chart going to 1600%, but because only one core is pinned, that one sits at 1/16th of the chart. This does not provide much useful information about why an application hangs, since it looks like it is hanging in IO instead of in a CPU loop.

Third, there is no actual unstacked line graph mode. The only option is a line mode with everything below it filled, which is very hard to read and to recognize patterns in (i.e. everything spiked to 100% but with some drops here and there to 0). KSysguard solved that by having the area below the line half transparent, which allowed you to see all the lines in any case.

STEPS TO REPRODUCE
1. Open CPU widget on a system with 16 cores or more

OBSERVED RESULT

Badly scaled CPU graph, that hides half the information.

EXPECTED RESULT

CPU graph that shows information of all CPU cores at a glance.

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 
(available in About System)
KDE Plasma Version: 5.21.2
KDE Frameworks Version: 5.79.0
Qt Version: 5.15.2
Comment 1 David Redondo 2021-03-08 09:58:22 UTC
FYI you can adjust the opacity of the fill color of the lines, for example the plasma widgets use more transparency by default
Comment 2 Arjen Hiemstra 2021-03-08 12:04:44 UTC
Please don't put multiple issues in one report, it makes it hard to deal with the individual issues.

> But KSysguard solved that more nicely, by first shrinking the legend to just colored percentages. You should still wrap them at some point, because otherwise 48 threads will fit on pretty much no screen, but having a colored line next to it is not very useful at that size.

This may be tweaked later, but KSysGuard's solution also does not scale too well and additionally has quite some contrast problems.

> Secondly, the default of using a stacked chart leads to a chart going to 1600%, but because only one core is pinned, that one sits at 1/16th of the chart. This does not provide much useful information about why an application hangs, since it looks like it is hanging in IO instead of in a CPU loop.

Seems to me this is better solved by the process table? How would you even distinguish single process usage from the history chart? In any case, stacked means you get to see individual core usage as well as overall usage and in my opinion it is actually easier to distinguish cores, even with lower fill opacity the screenshot of KSysGuard is pretty useless to me. That said, this is why the entire thing is configurable so you can choose not to use stacked (and as David said, you can also choose the fill opacity.)
Comment 3 Nate Graham 2023-04-03 20:28:43 UTC
*** Bug 442509 has been marked as a duplicate of this bug. ***
Comment 4 Nate Graham 2023-04-03 20:31:17 UTC
*** Bug 463761 has been marked as a duplicate of this bug. ***
Comment 5 Nate Graham 2023-04-03 20:41:34 UTC
Re-opening as we continue to accumulate complaints about this. It's notable that System Monitor has opposite default settings compared to ksysguard did: the CPU percentage in the list view is averaged rather than separate, while the CPU graph view is combined rather than averaged. It seems that people preferred the prior ksysguard default settings, not the new ones for System Monitor.
Comment 6 Bug Janitor Service 2023-04-03 21:39:49 UTC
A possibly relevant merge request was started @ https://invent.kde.org/plasma/plasma-systemmonitor/-/merge_requests/206
Comment 7 Nate Graham 2024-07-30 20:14:37 UTC
*** Bug 490895 has been marked as a duplicate of this bug. ***
Comment 8 TraceyC 2025-03-07 15:42:40 UTC
*** Bug 501152 has been marked as a duplicate of this bug. ***
Comment 9 Rob M 2025-04-05 18:14:47 UTC
Adding to the dogpile of complaints.  The way it worked in Ksysguard was better than System Monitor in Plasma 6.3.4.
Comment 10 Nate Graham 2025-05-08 17:40:29 UTC
In Plasma 6.4, there's now an averaged CPU usage graph on the History page!
Comment 11 Oliver Schramm 2025-11-27 03:32:01 UTC
*** Bug 512366 has been marked as a duplicate of this bug. ***