You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
84 lines
2.6 KiB
84 lines
2.6 KiB
8 years ago
|
From: Eric Dumazet <edumazet@google.com>
|
||
|
|
Date: Wed, 31 Aug 2016 10:42:29 -0700
|
||
|
|
Subject: [PATCH] softirq: let ksoftirqd do its job
|
||
|
|
|
||
|
|
A while back, Paolo and Hannes sent an RFC patch adding threaded-able
|
||
|
|
napi poll loop support : (https://patchwork.ozlabs.org/patch/620657/)
|
||
|
|
|
||
|
|
The problem seems to be that softirqs are very aggressive and are often
|
||
|
|
handled by the current process, even if we are under stress and that
|
||
|
|
ksoftirqd was scheduled, so that innocent threads would have more chance
|
||
|
|
to make progress.
|
||
|
|
|
||
|
|
This patch makes sure that if ksoftirq is running, we let it
|
||
|
|
perform the softirq work.
|
||
|
|
|
||
|
|
Jonathan Corbet summarized the issue in https://lwn.net/Articles/687617/
|
||
|
|
|
||
|
|
Tested:
|
||
|
|
|
||
|
|
- NIC receiving traffic handled by CPU 0
|
||
|
|
- UDP receiver running on CPU 0, using a single UDP socket.
|
||
|
|
- Incoming flood of UDP packets targeting the UDP socket.
|
||
|
|
|
||
|
|
Before the patch, the UDP receiver could almost never get cpu cycles and
|
||
|
|
could only receive ~2,000 packets per second.
|
||
|
|
|
||
|
|
After the patch, cpu cycles are split 50/50 between user application and
|
||
|
|
ksoftirqd/0, and we can effectively read ~900,000 packets per second,
|
||
|
|
a huge improvement in DOS situation. (Note that more packets are now
|
||
|
|
dropped by the NIC itself, since the BH handlers get less cpu cycles to
|
||
|
|
drain RX ring buffer)
|
||
|
|
|
||
|
|
Since the load runs in well identified threads context, an admin can
|
||
|
|
more easily tune process scheduling parameters if needed.
|
||
|
|
|
||
|
|
Reported-by: Paolo Abeni <pabeni@redhat.com>
|
||
|
|
Reported-by: Hannes Frederic Sowa <hannes@stressinduktion.org>
|
||
|
|
Signed-off-by: Eric Dumazet <edumazet@google.com>
|
||
|
|
Cc: David Miller <davem@davemloft.net
|
||
|
|
Cc: Jesper Dangaard Brouer <jbrouer@redhat.com>
|
||
|
|
Cc: Peter Zijlstra <peterz@infradead.org>
|
||
|
|
Cc: Rik van Riel <riel@redhat.com>
|
||
|
|
---
|
||
|
|
|
||
|
|
--- a/kernel/softirq.c
|
||
|
|
+++ b/kernel/softirq.c
|
||
|
|
@@ -78,6 +78,17 @@ static void wakeup_softirqd(void)
|
||
|
|
}
|
||
|
|
|
||
|
|
/*
|
||
|
|
+ * If ksoftirqd is scheduled, we do not want to process pending softirqs
|
||
|
|
+ * right now. Let ksoftirqd handle this at its own rate, to get fairness.
|
||
|
|
+ */
|
||
|
|
+static bool ksoftirqd_running(void)
|
||
|
|
+{
|
||
|
|
+ struct task_struct *tsk = __this_cpu_read(ksoftirqd);
|
||
|
|
+
|
||
|
|
+ return tsk && (tsk->state == TASK_RUNNING);
|
||
|
|
+}
|
||
|
|
+
|
||
|
|
+/*
|
||
|
|
* preempt_count and SOFTIRQ_OFFSET usage:
|
||
|
|
* - preempt_count is changed by SOFTIRQ_OFFSET on entering or leaving
|
||
|
|
* softirq processing.
|
||
|
|
@@ -313,7 +324,7 @@ asmlinkage __visible void do_softirq(voi
|
||
|
|
|
||
|
|
pending = local_softirq_pending();
|
||
|
|
|
||
|
|
- if (pending)
|
||
|
|
+ if (pending && !ksoftirqd_running())
|
||
|
|
do_softirq_own_stack();
|
||
|
|
|
||
|
|
local_irq_restore(flags);
|
||
|
|
@@ -340,6 +351,9 @@ void irq_enter(void)
|
||
|
|
|
||
|
|
static inline void invoke_softirq(void)
|
||
|
|
{
|
||
|
|
+ if (ksoftirqd_running())
|
||
|
|
+ return;
|
||
|
|
+
|
||
|
|
if (!force_irqthreads) {
|
||
|
|
#ifdef CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK
|
||
|
|
/*
|