diff options
| -rw-r--r-- | target/linux/generic/patches-4.4/061-softirq-let-ksoftirqd-do-its-job.patch | 83 |
1 files changed, 83 insertions, 0 deletions
diff --git a/target/linux/generic/patches-4.4/061-softirq-let-ksoftirqd-do-its-job.patch b/target/linux/generic/patches-4.4/061-softirq-let-ksoftirqd-do-its-job.patch new file mode 100644 index 0000000000..a2de48093c --- /dev/null +++ b/target/linux/generic/patches-4.4/061-softirq-let-ksoftirqd-do-its-job.patch @@ -0,0 +1,83 @@ +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 + /* |