ksoftirqd/X using CPU when system idle on recent kernels

rettw78 · 2015-04-01 16:47:41

Hi -

I have been looking for an explanation for this for some time. It would seem that kernels at least from the 3.18 and 3.19 series are showing a lot of soft irq traffic on two of my arch systems that wasn't present on earlier kernels.

running a top display on the machines show ksoftirqd/X (when X = the processor core) using small amounts of CPU pretty much constantly (top display below):

top - 11:19:04 up 27 days, 14:18,  7 users,  load average: 0.22, 0.37, 0.39
Tasks: 323 total,   1 running, 322 sleeping,   0 stopped,   0 zombie
%Cpu(s):   0.9/0.3     1[|                                                                                                   ]
GiB Mem : 26.8/15.574   [                                                                                                    ]
GiB Swap:  5.5/16.000   [                                                                                                    ]

  PID USER      PR  NI    VIRT    RES  %CPU %MEM     TIME+ S COMMAND
   55 root      20   0    0.0m   0.0m   5.3  0.0 462:18.36 S ksoftirqd/9
   45 root      20   0    0.0m   0.0m   3.3  0.0 477:34.26 S ksoftirqd/7
   65 root      20   0    0.0m   0.0m   3.3  0.0 415:43.78 S ksoftirqd/11
   50 root      20   0    0.0m   0.0m   2.6  0.0 525:43.15 S ksoftirqd/8
   14 root      20   0    0.0m   0.0m   2.0  0.0 128:27.55 S ksoftirqd/1
   40 root      20   0    0.0m   0.0m   2.0  0.0 638:32.30 S ksoftirqd/6
 9180 rettw     20   0 2663.2m 1.320g   2.0  8.5   6:06.25 S VBoxHeadless
 9290 rettw     20   0 1781.3m 526.8m   2.0  3.3   1:39.90 S VBoxHeadless
    3 root      20   0    0.0m   0.0m   1.3  0.0 390:41.97 S ksoftirqd/0
   25 root      20   0    0.0m   0.0m   1.3  0.0 108:40.02 S ksoftirqd/3
 9236 rettw     20   0 1588.0m 371.6m   1.3  2.3   0:57.24 S VBoxHeadless

I have this on two systems running the latest arch kernels here are the specs:

I5930K (Standard Clock) w/ 16GB DDR 4 2133 RAM w/LSI SAS2008 8 port controller
MSI X99 SLI-Plus Motherboard
EVGA GTX 470 Video card (using nvidia blob drivers arch package)

Second system:

I3930K (Overclocked to 4.2Ghz) w/ 16GB DDR3 1600 RAM
Asus X79 Sabertooth Motherboard
MSI GTX 970 Video Card (using nvidia binary blob driver arch package)

I also have an Asus G750 Laptop that doesn't exhibit the issue:

i7-4700HQ CPU /32 GB DDR3
GTX 770M Video chip (using nvidia blob drivers arch package)

These machines are running very similar software - Latest KDE, Latest arch Kernel 3.19, Virtualbox kernel modules, Nvidia Blob drivers. The laptop and the i3930k machine have Vmware workstation kernel drivers loaded as well. problem still occurs when X and apps/vms are stopped and the machines are sitting at a console (but still in multi-user mode). The i5930K machine is a brand new install of arch, while the others have been running for 1-3 years with regular updates.

Haven't noticed any other abnormal behavior - just seems odd that there would be this much soft irq traffic on idle systems that don't have a lot going on.

Any thoughts on this would be appreciated - Spent a lot of time searching for answers, but no one seems to have noticed this.

Thinking about maybe trying to revert back to an earlier kernel to see if I can figure out where it changed...

Thanks,

Rett Walters

rettw78 · 2015-04-01 18:18:47

Well - after posting this I dug in a bit more, and I think I found the culprit - x2goserver. Stopping x2goserver eliminates most of the soft irq traffic.

I still think this is related to some interaction between this software and the kernel, since it seem like it wasn't there before 3.18.

I will post something on the X2go mailling list to see if I get a response.

Rett

Arch Linux

#1 2015-04-01 16:47:41

ksoftirqd/X using CPU when system idle on recent kernels

#2 2015-04-01 18:18:47

Re: ksoftirqd/X using CPU when system idle on recent kernels

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