[linuxdc-dev] swapping to vram

[Alex W. <ale...@at...>]

    I started playing with using the extra video ram on the dc for swap
after someone pointing me this article:

http://hedera.linuxnews.pl/_news/2002/09/03/_long/1445.html

As I'm sure many of you know, there's 8192k of video memory on the dc,
and if you're only using an unaccellerated 640x480x16 framebuffer,
you're only using 600k of that.  To prove that it's worthwhile, I've
run some performance numbers.  All of these are simply timing a kernel
build, doing a make clean, and swapoff/swapon in between.  If I were
on a system w/ more memory maybe I would have worried about buffer
cache but I don't think it's important here.  I'm running the 7/28
base + updates from debian.dodes.org using nfsroot.  I'm also using
a 2.4.18 kernel + linux-sh + linux-sh-dc + nfs-swap.  Here's the
data:

NFS swap, make clean, make zImage
real    80m35.143s
user    63m6.430s
sys     4m48.220s


VRAM swap + NFS swap, make clean, make zImage
real    72m0.480s
user    62m54.910s
sys     3m57.560s

~10% improvement, not bad.  Now if your system really gets hammered:

NFS swap, make clean, MAKE="make -j2" make zImage
real    367m50.110s
user    67m32.910s
sys     231m31.150s

VRAM swap + NFS swap, make clean, MAKE="make -j2" make zImage
real    292m53.256s
user    66m57.060s
sys     174m9.540s

~20% improvement!  This is likely the worst I've pounded the dc.
In most cases, just building debian packages, the most I've seen
are 2 compiles running at once.  The parallel build can do parallel
across directories, so more the 2 things can be going at once.

Here's some snippets of my config if you want to reproduce:

/etc/modules
mtdblock
slram
blkdev_swap

/etc/modutils/slram
options slram map=VRAM,0xa5096000,+0x76a000
post-install slram /sbin/mkswap /dev/mtdblock0

/etc/fstab
/dev/mtdblock0                        none           swap sw,pri=1 0 0
/swap/swap                            none           swap sw,pri=0 0 0

(/swap/swap is my nfs swap)

I'm not on the list, so please CC for followup.  Have fun,

	Alex