[gentoo-performance] Horrible performance

[Alex Schuster]

Me again.

I wrote here about my problems with mplayer stuttering during emerges. 
Then I wrote that the problem went away when I installed Gentoo again, 
moving from i686 to x86_64. But the problems are back, and worse than 
ever. This is driving me crazy. CRAZY!

I have an AMD Athlon(tm) Dual Core Processor 4850e CPU, on-board Radeon HD 
3200 graphics, 4GB of memory, an 1.5 TB drive. Lots of LVM volumes, all 
encrypted, except for /usr/src and portage stuff. The system is ~amd64, 
and I have -march=k8-sse3 in my CFLAGS. Current kernel is 2.6.34-tuxonice, 
but I also tried others. I'm running KDE4 with desktop effects enabled, X 
itself takes about 30-40% of CPU time according to top. After system 
startup and login into KDE, 3.5G of RAM are occupied. This increases after 
a while, and I need swap space. Nothing to worry about I think.

Performance does not feel too bad at first. But after a while, I cannot 
even play videos during emerges. The playback stutters, sometimes I have 
pauses for several seconds. As long as there is no swap space occpied, 
it's not so bad I think. Maybe I have a probelm with disk I/O, and things 
get much worse when swapping occurs. When I look at iotop, I see 
various programs like chromium and various KDE applications appear. I 
guess that's normal, but should not be noticeable. Hey, there were times 
when I created a 2G tmpfs for /var/tmp/portage, with only 3G on 
my 32bit system. BTW, I lowered my swappiness to 10. This helps a little I 
think, because the swapping occurs later, the system is more responsive.

And it feels like things get worse and worse, it's not like there was a 
specific point when I thought it's slow again. Like there were some 
degragation going on - fragmentation, bitrot, I don't know. It's just how 
it feels to me.

I am debugging this for some days now. I tried different kernels, from 
2.6.29 to 2.6.35, including the kernel I had running after the switch to 
64bit, when I thought all was fine. No change. But all kernels were 
configured nearly identical, so I booted a GRML live-cd and used this 
kernel .config as a template. Does not feel better.

When I thought the problem was gone, I had installed the system on my 2nd 
1.5 TB drive. Meanwhile I copied the partitions back to the 1st drive, so 
I suspected a difference in the drives. I use the 2nd drive for backups 
(using rdiff-backup), with similar partitions, so I only have to exchange 
the LVM volume group names of the two drives in order to run my system 
from the 2nd one. I tried this, but it did not help.

And I have similar problems when copying data between some old PATA 
drives. When I copy stuff and do a mkfs on another partition, mplayer 
sometimes stutters and hangs for ten seconds. No joy. Working with KDE 
sucks, switching dektops sometimes takes ages, and even now I am typing 
faster than kmail can display the characters. That's with am emerge of 
chromium running, with PORTAGE_NICENESS=10 and using ionice -c 3. Load is 
around 8, but sometimes gets even higher. And then, load suddenly drops 
back to lower values, as if somthing was blocking. Some applications 
swapping, maybe. 

Now I am out of ideas. I really hope someone here has one. I cannot work 
with this system any more when emerges are going on.

I put my kernel config, make.conf, dmesg and such stuff to 
http://www.wonkology.org/gentoo/ in case someone wants to have a look at 
it. Any help is GREATLY appreciated.

	Wonko