netdev - Re: [RFC] NAPI behavior when (work

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Message-ID: <1423057029.907.133.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Wed, 04 Feb 2015 05:37:09 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Vladimir Kondratiev <QCA_vkondrat@....qualcomm.com>
Cc:	netdev@...r.kernel.org, "David S. Miller" <davem@...emloft.net>,
	Herbert Xu <herbert@...dor.apana.org.au>,
	Eric Dumazet <edumazet@...gle.com>,
	Tom Herbert <therbert@...gle.com>,
	Vlad Yasevich <vyasevic@...hat.com>,
	Jiri Pirko <jiri@...nulli.us>,
	John Fastabend <john.fastabend@...il.com>,
	Joe Perches <joe@...ches.com>
Subject: Re: [RFC] NAPI behavior when (work < weight)

On Wed, 2015-02-04 at 15:22 +0200, Vladimir Kondratiev wrote:
> Hi
> 
> I am observing that if driver does not calls napi_complete() when
> less than full budget consumed, various strange things happen.
> 
> For example, if driver going to napi_disable(), it may wait forever
> in the loop:
> 
> 	while (test_and_set_bit(NAPI_STATE_SCHED, &n->state))
> 		msleep(1);
> 
> if last NAPI consumed less then full budget, because bit
> NAPI_STATE_SCHED never cleared.
> 
> Is it expected that driver calls napi_complete() when less than full
> budget consumed? Documentation does not say so.
> 
> What is intended behavior in case above?

A driver must call napi_complete() (or better : napi_complete_done() )
when/if returning work_done < budget

Thats because of the way we have to rearm interrupts in the driver,
_after_ calling napi_complete()



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