From: Ingo Molnar <redacted>
Date: Thu, 24 Jul 2008 11:25:18 +0200

ok, i've booted the latest kernel on dione and the builds are running on 
it now. It's using these settings currently:

 # cat /proc/sys/net/ipv4/tcp_syncookies
 0
 # cat /proc/sys/net/ipv4/tcp_sack
 1

Just to make sure i have the right test-plan: assuming this 
suspected-good kernel is trouble-free for say 48 hours, i should be able 
to switch back to the suspected-broken variant, by doing:

   echo 1 > /proc/sys/net/ipv4/tcp_syncookies

without rebooting the kernel, right? And then if the bug comes back 
again we've nailed it down to the area you suspect, correct?

You don't need the explicit tcp_sack=1, it's going to be '1' by
default.

Simply switching syncookies on and off will turn both SACK and
timestamps off when running the dist kernel.