On Fri, May 13, 2016 at 9:50 AM, Paolo Abeni <pab...@redhat.com> wrote:
>> Indeed, and the patch looks quite simple now ;)
>>
>> diff --git a/kernel/softirq.c b/kernel/softirq.c
>> index
>> 17caf4b63342d7839528f367b283a386413b0362..23c364485d03618773c385d943c0ef39f5931d09
>> 100644
>> --- a/kernel/softirq.c
>> +++ b/kernel/softirq.c
>> @@ -57,6 +57,11 @@ static struct softirq_action softirq_vec[NR_SOFTIRQS]
>> __cacheline_aligned_in_smp
>>
>> DEFINE_PER_CPU(struct task_struct *, ksoftirqd);
>>
>> +static inline bool ksoftirqd_running(void)
>> +{
>> + return __this_cpu_read(ksoftirqd)->state == TASK_RUNNING;
>> +}
>> +
>> const char * const softirq_to_name[NR_SOFTIRQS] = {
>> "HI", "TIMER", "NET_TX", "NET_RX", "BLOCK", "BLOCK_IOPOLL",
>> "TASKLET", "SCHED", "HRTIMER", "RCU"
>> @@ -313,7 +318,7 @@ asmlinkage __visible void do_softirq(void)
>>
>> pending = local_softirq_pending();
>>
>> - if (pending)
>> + if (pending && !ksoftirqd_running())
>> do_softirq_own_stack();
>>
>> local_irq_restore(flags);
>> @@ -340,6 +345,9 @@ 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
>> /*
>
> In this version of the path, the chunk affecting __local_bh_enable_ip()
> has been removed.
>
> I think it is beneficial, because it allows avoiding a
> local_irq_save()/local_irq_restore() pairs per local_bh_enable under heavy
> load.
>
Interesting, do you have any numbers ?
I believe I did this so that we factorize the logic in do_softirq()
and keep the code local to kernel/softirq.c
Otherwise, netif_rx_ni() could also process softirq while ksoftirqd
was scheduled,
so I would have to 'export' the ksoftirqd_running(void) helper in an
include file.
I noticed that simply doing a "ping -n gateway" while the UDP flood
was occurring, my udp receiver had quite a different efficiency.
Thanks.
