Re: X mysteriously slow, no clue why

[Andrew Schulman <andrex@alumni.utexas.net>]

> I have this REALLY weird problem right now. My whole X has suddenly
> started to be really slow. KDE used to be really snappy and nice to
> use, now it's really sluggish and slow to respond.

Have you changed your firewall settings lately?  This slowness happened to
me once when, by mistake, I set the default policy in the iptables nat and
mangle tables to DROP.  That stopped all traffic on the loopback interface,
which made my whole system (but especially KDE) slow to a crawl.  Took me
about a week to figure it out.

You can check this easily.  Run the following commands as root:

# Allow all traffic to pass on the loopback interface
iptables -A INPUT  -i lo   -j ACCEPT
iptables -A OUTPUT -o lo   -j ACCEPT

# Set default ACCEPT policies on the nat and mangle tables
iptables -t nat --policy PREROUTING  ACCEPT
iptables -t nat --policy POSTROUTING ACCEPT
iptables -t nat --policy OUTPUT      ACCEPT
iptables -t mangle --policy PREROUTING  ACCEPT
iptables -t mangle --policy INPUT       ACCEPT
iptables -t mangle --policy FORWARD     ACCEPT
iptables -t mangle --policy OUTPUT      ACCEPT
iptables -t mangle --policy POSTROUTING ACCEPT

Good luck,
Andrew.