Dipankar Sarma writes:

 > Looks better atleast. Can you apply the following patch (rs-throttle-rcu)
 > on top of rcu-softirq.patch in your tree and see if helps a little bit more ?
 > Please make sure to set the kernel paramenters rcupdate.maxbatch to 4
 > and rcupdate.plugticks to 0. You can make sure of those parameters
 > by looking at dmesg (rcu prints them out during boot). I just merged
 > it, but have not tested this patch yet.

OK!

Well not tested yet but I don't think we will get rid overflow totally in my 
setup. I've done a little experimental patch so *all* softirq's are run via 
ksoftirqd. 
 
 total    droppped tsquz    throttl  bh_enbl  ksoftird irqexit  other  
009bee0c 00000000 00004aa7 00000000 00000000 0336a637 00000078 00000000
0054d381 00000000 00004ca0 00000000 00000000 032f8e48 00000000 00000000

I still see dst overflows. But the priority of the ksoftird's can now control 
the user apps behavior even during softirq DoS.