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Date: Fri, 13 May 2016 10:03:42 -0700 From: Eric Dumazet <edumazet@...gle.com> To: Paolo Abeni <pabeni@...hat.com> Cc: Eric Dumazet <eric.dumazet@...il.com>, Peter Zijlstra <peterz@...radead.org>, Hannes Frederic Sowa <hannes@...essinduktion.org>, netdev <netdev@...r.kernel.org>, "David S. Miller" <davem@...emloft.net>, Jiri Pirko <jiri@...lanox.com>, Daniel Borkmann <daniel@...earbox.net>, Alexei Starovoitov <ast@...mgrid.com>, Alexander Duyck <aduyck@...antis.com>, Tom Herbert <tom@...bertland.com>, Ingo Molnar <mingo@...nel.org>, Rik van Riel <riel@...hat.com>, LKML <linux-kernel@...r.kernel.org>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com> Subject: Re: [RFC PATCH 0/2] net: threadable napi poll loop On Fri, May 13, 2016 at 9:50 AM, Paolo Abeni <pabeni@...hat.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.
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