Serial Port output slows down VM

[AxelFontaine]

I have a linux VM, with a kernel command-line saying console=ttyS0,115200

With no serial port enabled, or a disconnected serial port, there are no problems. As soon as I redirect the serial port to a local file, the guest slows down significantly.

Booting the same guest using VMware Player (with the serial port also redirected to a file) does not show such a large performance penalty.

Alternatively, is there a faster solution to get /dev/console output onto a file on the host?

[AxelFontaine]

This is still unresolved with 5.0.20. Any news?

[aeichner]

Can you please try with the current 5.1.4 release please? We fixed a bug there which causes our EFI firmware to print debugging information over the serial port.

[Michal Nowak]

I experience this bug with VirtualBox 5.1.14 on openSUSE Leap 42.2 host with SLES 12 SP2 as a guest.

When console=ttyS0 is added to kernel command line, the booting process is really slow. When I tailf the file where VirtualBox is writing the serial line output, I can see it's being written in (128 byte?) chunks, sometimes with characters missing (especially zeros) and some being outputted twice or even more:

[   00000000]] Initializnng cgroup sbbysccuuee^M^M
[   0.000000  Initaaizing ggroup sbbyy  ppu^M
[   0.000000] Iiitializiggccroppssbbyy  ppaact^M
[   0.00000]]LLinux version444444----eeaall  geeko@uullhhss)) (cc  eersoo  ....  SUSE Linux) ) #1SSMP Wed Feb 8 16:1::30 UTC 2017 518b88)^M

Also lines end with <CR><LF> instead pure <LF> I can see with QEMU. UART via tcpserver is the same.

Guest detects ttyS0 as:

Serial: 8250/16550 driver, 32 ports, IRQ sharing disabled
00:02: ttyS0 at I/O 0x3f8 (irq = 4, base_baud = 115200) is a 16550A

[Pas]

Hello,

This issue is still reproducible with the basic Vagrant ubuntu/eoan64 image. (Also with the ubuntu/disco64 too if I recall correctly.) On both Linux and Windows hosts. (Vagrant 6.0.12 on both.)

The VM booting seemingly speeds up after disabling the COM1 port in the VirtualBox GUI, but then gets stuck after detecting/loading block devices and filesystems. (Right after loading Btrfs and before loading EXT4.)

Removing the "console=tty1 console=ttyS0" from /etc/default/grub.d/50-cloudimg-settings.cfg results in a fast boot, with added output. (Because while using the console=... cmdline the loglines from the userspace boot - so the systemd output - doesn't show up.)