netdev - Re: [RFC PATCH 0/2] net: threadable napi poll loop

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Message-ID: <1462981808.23934.145.camel@edumazet-glaptop3.roam.corp.google.com>
Date:	Wed, 11 May 2016 08:50:08 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Eric Dumazet <edumazet@...gle.com>
Cc:	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Paolo Abeni <pabeni@...hat.com>,
	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>
Subject: Re: [RFC PATCH 0/2] net: threadable napi poll loop

On Wed, 2016-05-11 at 07:40 -0700, Eric Dumazet wrote:
> On Wed, May 11, 2016 at 6:13 AM, Hannes Frederic Sowa
> <hannes@...essinduktion.org> wrote:
> 
> > This looks racy to me as the ksoftirqd could be in the progress to stop
> > and we would miss another softirq invocation.
> 
> Looking at smpboot_thread_fn(), it looks fine :
> 
>                 if (!ht->thread_should_run(td->cpu)) {
>                         preempt_enable_no_resched();
>                         schedule();
>                 } else {
>                         __set_current_state(TASK_RUNNING);
>                         preempt_enable();
>                         ht->thread_fn(td->cpu);
>                 }

BTW, I wonder why we pass td->cpu as argument to ht->thread_fn(td->cpu)

This always should be the current processor id.

Or do we have an issue because we ignore it in :

static int ksoftirqd_should_run(unsigned int cpu)
{
        return local_softirq_pending();
}