netdev - Re: [PATCH net-next 0/2] sunvnet: Packet processing in non-interrupt context.

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Message-Id: <20141001.162529.2246298941833907545.davem@davemloft.net>
Date:	Wed, 01 Oct 2014 16:25:29 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	sowmini.varadhan@...cle.com
Cc:	raghuram.kothakota@...cle.com, netdev@...r.kernel.org
Subject: Re: [PATCH net-next 0/2] sunvnet: Packet processing in
 non-interrupt context.

From: Sowmini Varadhan <sowmini.varadhan@...cle.com>
Date: Wed, 1 Oct 2014 16:23:15 -0400

> On (10/01/14 16:15), David Miller wrote:
>> > 
>> > If I make this a NAPI driver that uses napi_gro_receive, I would
>> > still have to deal with a budget, right?
>> 
>> Absolutely, and YOU MUST, because the budget keeps one device from
>> hogging the RX packet input path from other devices on a given cpu.
> 
> yes, but limiting the budget of sk_buffs read mid-way during descriptor
> read is deadly to perf because of the ensuing LDC stop/start exchange -
> ends up being even worse than the baseline.
> 
> Doesnt the netif_rx/process_backlog infra already do a napi_schedule,
> thus avoiding the above concern? 

The limit is by default 64 packets, it won't matter.

I think you're overplaying the things that block use of NAPI, how
about implementing it properly, using netif_gso_receive() and proper
RCU accesses, and coming back with some real performance measurements?
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