netdev - Re: [PATCH net-next 16/16] sfc: Don't receive packets when the napi budget == 0

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Message-ID: <874n2znu25.fsf@xmission.com>
Date:	Sat, 15 Mar 2014 12:25:06 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Ben Hutchings <ben@...adent.org.uk>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	xiyou.wangcong@...il.com, mpm@...enic.com, satyam.sharma@...il.com
Subject: Re: [PATCH net-next 16/16] sfc: Don't receive packets when the napi budget == 0

Eric Dumazet <eric.dumazet@...il.com> writes:

> On Sat, 2014-03-15 at 17:23 +0000, Ben Hutchings wrote:
>
>> The Solarflare hardware provides generic event queues for RX and TX
>> completions, link changes, errors, etc.  The driver can't process TX
>> completions without going through all the other events mixed in with
>> them.
>> 
>
> ndo_poll_controller() could process all events, and queue incoming
> packets through netif_rx().
>
> Nobody cares about performance in this path.

I made this change so that we don't process rx packets in hard irq
context and cause things to break, and I made the most minimal most
obvious change I could.

queueing incoming packets with trough netif_rx sounds elegant.

The practical challenge is that there might be napi bottom halves
already scheduled to run before ndo_poll_controller is called so even
if ndo_poll_controller processes all of the events and calls netif_rx
to deal with the incoming packets the napi bottom halves will have to
still not process the queues when they are called.

Eric

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