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SubjectRe: [patch] softirq performance fixes, cleanups, 2.4.10.
On Fri, 28 Sep 2001 20:18:20 +0400 (MSK DST)
kuznet@ms2.inr.ac.ru wrote:

> Also, you did not assure me that you interpret problem correctly.
> netif_rx() is __insensitive__ to latencies due to blocked softirq
restarts.
> It stops spinning only when it becomes true cpu hog. And scheduling
ksoftirqd
> is the only variant here.

Hi Ingo at al,

Attached is the approach I sent to l-k earlier this week: if a timer tick
goes off, back off to ksoftirqd.

This should, statistically, do the right thing, even in the case of smart
softirqs like netif_rx.

Please consider,
Rusty.

--- linux-pmac/kernel/softirq.c Sun Sep 9 15:11:37 2001
+++ working-pmac-ksoftirq/kernel/softirq.c Mon Sep 24 09:44:07 2001
@@ -63,11 +63,12 @@
int cpu = smp_processor_id();
__u32 pending;
long flags;
- __u32 mask;
+ long start;

if (in_interrupt())
return;

+ start = jiffies;
local_irq_save(flags);

pending = softirq_pending(cpu);
@@ -75,32 +76,32 @@
if (pending) {
struct softirq_action *h;

- mask = ~pending;
local_bh_disable();
-restart:
- /* Reset the pending bitmask before enabling irqs */
- softirq_pending(cpu) = 0;
+ do {
+ /* Reset the pending bitmask before enabling irqs */
+ softirq_pending(cpu) = 0;

- local_irq_enable();
+ local_irq_enable();

- h = softirq_vec;
+ h = softirq_vec;

- do {
- if (pending & 1)
- h->action(h);
- h++;
- pending >>= 1;
- } while (pending);
-
- local_irq_disable();
-
- pending = softirq_pending(cpu);
- if (pending & mask) {
- mask &= ~pending;
- goto restart;
- }
+ do {
+ if (pending & 1)
+ h->action(h);
+ h++;
+ pending >>= 1;
+ } while (pending);
+
+ local_irq_disable();
+
+ pending = softirq_pending(cpu);
+
+ /* Don't spin here forever... */
+ } while (pending && start == jiffies);
__local_bh_enable();

+ /* If a timer tick went off, assume we're overloaded,
+ and kick in ksoftirqd */
if (pending)
wakeup_softirqd(cpu);
}

-
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