Arch Linux

MasterKTO

Member

Registered: 2020-09-23

Posts: 2

Disk I/O performance problem on VirtualBox with kernel 4.18+

Hello,

I have the following problem for some time now on my Lenovo ThinkPad T550 (Intel Core i5-5300U):

In short

When using Linux kernel 4.18+, I have terrible performance with VirtualBox when it comes to disk I/O.

More details

Kernel version: No issue with kernels up to 4.15. The problem occurs when using any 4.18 or newer kernel. I don't know for 4.16 & 4.17 (they're not maintained for some time now), but I can try them should it be of any help.

VirtualBox versions do not seem to be of any impact. I currently run 6.1.14.

In order to test correctly, I did the following:

• Created a VM and installed Ubuntu 20.04 (from mini.iso, only basic system), then waited for the first kernel update;

• Downloaded but not installed the updated packages;

• Kept the VM in this state (I still do), then cloned it for each of my tests;
      * I have both SSD and HDD on the computer, and as I run Arch Linux, I tested with the following configurations:
      * Host kernel 5.8 and VM on SSD;
      * Host kernel 5.8 and VM on HDD;
      * Host kernel 4.14 and VM on SSD;
      * Host kernel 4.14 and VM on HDD;

• My test was to run `apt upgrade` and measure time between the moment I hit the Enter key and the moment the upgrade process is done and I get the prompt back.

Test results:

• 5.8 SSD: 9 min

• 5.8 HDD: 33 min (!!)

• 4.14 SSD: 2 min 45 sec

• 4.14 HDD: 3 min 15 sec

As you can see, the figures are quite evoking... This 3-minute operation takes 3 to 11 times the same time with recent kernels.

This forum may not be the right place for this issue (apologies in that case), but I hope some of you can give me hints on how to solve this problem: Do you think as I do that it is about disk I/O? Should I raise this to a kernel mailing list?

Thank you in advance for your time, and for your lights!

Last edited by MasterKTO (2020-09-23 15:08:22)

V1del

Forum Moderator

Registered: 2012-10-16

Posts: 21,738

Re: Disk I/O performance problem on VirtualBox with kernel 4.18+

This reads like this was probably around the time the scheduler defaults got switched to the MQ set of schedulers. Play with those: https://wiki.archlinux.org/index.php/Improving_performance#Kernel's_I/O_schedulers

Of the available options BFQ is generally mostly in line with the previous default of CFQ.

MasterKTO

Member

Registered: 2020-09-23

Posts: 2

Re: Disk I/O performance problem on VirtualBox with kernel 4.18+

Thanks W1del for your quick response.

I have been reading this very instructive wiki page and playing with the available schedulers for the past few days.

First of all, I noticed that the default scheduler used by my 4.14 kernel is Deadline, not CFQ. Regardless, I tried the four solutions available with modern kernels, the multi-queue schedulers.

Whether I use mq-deadline (the default, used for my previous measure), None, BFQ or Kyber, the results are quite similar;
mq-deadline being the best with 9 min for SSD and 33 min for HDD, and None being the worst with 10 min for SSD and 35 min for HDD.

I would then exonerate the schedulers, unless the problem is the use of multi-queue in the first place...