Re: route cache DoS testing and softirqs

[Robert Olsson <Robert.Olsson@data.slu.se>]

[-- Attachment #1: message body text --]
[-- Type: text/plain, Size: 961 bytes --]


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.


[-- Attachment #2: softirq_limit-040405.pat --]
[-- Type: application/octet-stream, Size: 1481 bytes --]

--- kernel/softirq.c.orig	2004-03-11 03:55:24.000000000 +0100
+++ kernel/softirq.c	2004-04-05 12:52:40.000000000 +0200
@@ -58,6 +58,14 @@
 		wake_up_process(tsk);
 }
 
+static inline int can_run_ksoftirqd(void)
+{
+       /* Interrupts are disabled: no need to stop preemption */
+       struct task_struct *tsk = __get_cpu_var(ksoftirqd);
+
+       return tsk && !(tsk->state &  (TASK_DEAD | TASK_ZOMBIE));
+}
+
 /*
  * We restart softirq processing MAX_SOFTIRQ_RESTART times,
  * and we fall back to softirqd after that.
@@ -69,7 +77,7 @@
  */
 #define MAX_SOFTIRQ_RESTART 10
 
-asmlinkage void do_softirq(void)
+asmlinkage void __do_softirq(int from_ksoftirqd)
 {
 	int max_restart = MAX_SOFTIRQ_RESTART;
 	__u32 pending;
@@ -86,6 +94,9 @@
 		struct softirq_action *h;
 
 		local_bh_disable();
+
+		if (from_ksoftirqd && can_run_ksoftirqd())
+			     goto done;
 restart:
 		/* Reset the pending bitmask before enabling irqs */
 		local_softirq_pending() = 0;
@@ -106,6 +117,7 @@
 		pending = local_softirq_pending();
 		if (pending && --max_restart)
 			goto restart;
+done:
 		if (pending)
 			wakeup_softirqd();
 		__local_bh_enable();
@@ -114,6 +126,11 @@
 	local_irq_restore(flags);
 }
 
+asmlinkage void do_softirq(void) 
+{
+	__do_softirq(0);	
+}
+
 EXPORT_SYMBOL(do_softirq);
 
 void local_bh_enable(void)
@@ -324,7 +341,7 @@
 		__set_current_state(TASK_RUNNING);
 
 		while (local_softirq_pending()) {
-			do_softirq();
+			__do_softirq(1);	
 			cond_resched();
 		}
 

[-- Attachment #3: message body text --]
[-- Type: text/plain, Size: 19 bytes --]



Cheers.
					--ro