Soft scrollback for the Linux VGA console

If you're a heavy user of the Linux VGA console, you'll like this feature. Recent 2.6 kernels have added support for soft scrollback. This feature enables you to have much bigger scrollback buffer than the standard console has, at the price of slightly slower console output.

The scrollback buffer of the standard VGA console is located in VGA RAM. This RAM is fixed in size and is very small. To make the scrollback buffer larger, it must be placed instead in System RAM. We call this soft scrollback.

The feature and the size of the buffer are enabled/configured through kernel config options, during kernel compilation. Beside consuming kernel memory, enabling this feature will slow down the console by approximately 20%.

If you want this feature, say "Y" to VGACON_SOFT_SCROLLBACK kernel config item, and then enter the amount of System RAM to allocate for the scrollback buffer (VGACON_SOFT_SCROLLBACK_SIZE). Each 64KB will give you approximately 16 80x25 screenfuls of scrollback buffer.

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Why using it?

Ridiculous article!
I'm quite heavy user of tty consoles but I don's see why should I "Slowing down the console"?

/admir

No the comment is ridiculous,

No the comment is ridiculous, not the article.

It may not suit you, fine, but it may suit others. The article explains the advantages and disadvantages so you can make an informed choice according to your own needs and preferences.

I tried this but it didn't seem to work

I'm using the 2.6.20-gentoo-r7 kernel on amd64. I think these are the relavant kernel options:

$ zgrep SCROLL /proc/config.gz
CONFIG_VGACON_SOFT_SCROLLBACK=y
CONFIG_VGACON_SOFT_SCROLLBACK_SIZE=640

$ zgrep ^CONFIG_FB /proc/config.gz
CONFIG_FB=y
CONFIG_FB_CFB_FILLRECT=y
CONFIG_FB_CFB_COPYAREA=y
CONFIG_FB_CFB_IMAGEBLIT=y
CONFIG_FB_MODE_HELPERS=y
CONFIG_FB_VESA=y
CONFIG_FB_VESA_STD=y
CONFIG_FB_SPLASH=y

There has been no change in the number of screenfulls I can scrollback which is currently about seven. Any suggestions?

History, of course

I don't think that 20% slowdown is something that you would notice that much. OTOH, screen history is priceless during some tasks.

Why don't you try for yourself and see if the slowdown is actually noticeable?

scrollback buffer after console switch

Hi all,
I'm actually searching for a scrollback buffer issue:
If I switch virtual console (Alt+Fn), the scrollbackbuffer is cleared. Is there a way to let the buffer untouched?
regards
Thomas