Bug 461745

Summary:	doesn't report correct speed on btrfs raid 0 volume
Product:	[Frameworks and Libraries] ksystemstats	Reporter:	sp <sp139>
Component:	General	Assignee:	KSysGuard Developers <ksysguard-bugs>
Status:	REPORTED ---
Severity:	normal	CC:	ahiemstra, kde, plasma-bugs-null
Priority:	NOR
Version First Reported In:	unspecified
Target Milestone:	---
Platform:	Neon
OS:	Linux
Latest Commit:		Version Fixed/Implemented In:
Sentry Crash Report:

Description sp 2022-11-12 21:53:42 UTC

SUMMARY

When drive/mountpoint to monitor is in btrfs raid0, read and writes speeds are incorrect (seems to take only one of the drives in that raid)

DETAILS:
In my current case there's 2 drives in raid0 and plasma system Monitor reports half the speed.

REPLICATE:

-have 2 free devices/partitions (for ex: sda2 sdb2)
-create the raid with them (mkfs.btrfs -L raid-test -d raid0 -m raid0 -f /dev/sda2 /dev/sdb2)
-mount the raid (mount LABEL=raid-test /mountpoint)

Monitor that mountpoint while doing read/writes (for write example: dd if=/dev/zero of=/mountpoint/GBfile bs=1M count=4096 oflag=nocache conv=fdatasync status=progress )

expected behaviour:
the write (or read) speed should obviously be faster than a single drive

behaviour:
speed displayed is as if only one drive was used

Operating System: KDE neon 5.26
KDE Plasma Version: 5.26.0
KDE Frameworks Version: 5.99.0
Qt Version: 5.15.7
Kernel Version: 5.15.0-52-generic (64-bit)
Graphics Platform: X11
Processors: 12 × Intel® Core™ i7-3930K CPU @ 3.20GHz
Memory: 62.7 GiB of RAM
Graphics Processor: NVIDIA GeForce GTX 980/PCIe/SSE2

Comment 1 David Redondo 2023-01-11 10:42:29 UTC

Can you confirm the real speed is higher than the one plasma-systemmonitor shows?

Comment 2 sp 2023-01-11 16:29:16 UTC

(In reply to David Redondo from comment #1)
> Can you confirm the real speed is higher than the one plasma-systemmonitor
> shows?

Yes, the real speed is higher than the one plasma-systemmonitor shows.
Running for example the dd command , plasma says at max around 490MB/s,  dd around 900+ and gkrellm around 900+.

Noticed something that could be related or a clue. Benchmarking with kdiskmark I used to have the same symptoms thaN plasma until I unchecked, in preferences, O_DIRECT.

Comment 3 David Redondo 2023-01-12 08:05:29 UTC

Thanks