netdev - Re: [RFC PATCH] udp: allow busy_poll on some unconnected sockets

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Message-ID: <1397156649.16584.45.camel@edumazet-glaptop2.roam.corp.google.com>
Date:	Thu, 10 Apr 2014 12:04:09 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Edward Cree <ecree@...arflare.com>
Cc:	netdev@...r.kernel.org, Shawn Bohrer <shawn.bohrer@...il.com>,
	Shawn Bohrer <sbohrer@...advisors.com>,
	Jonathan Cooper <jcooper@...arflare.com>
Subject: Re: [RFC PATCH] udp: allow busy_poll on some unconnected sockets

On Thu, 2014-04-10 at 19:38 +0100, Edward Cree wrote:
> On 10/04/14 19:32, Eric Dumazet wrote:
> > On Thu, 2014-04-10 at 19:04 +0100, Edward Cree wrote:
> >
> >> Tested by setting IFF_SINGLE_NAPI in sfc; a UDP ping-pong test showed a
> >>  performance benefit from sysctl net.core.busy_{read,poll}=50 in both the
> >>  connected and unconnected case, where previously it only saw the benefit
> >>  when the socket had been connected.
> > Right, but how often do we have single NAPI devices on hosts wanting
> > very low latencies ?
> >
> Well, sfc only has a single NAPI context per device, and I'm fairly sure
> most sfc users want very low latencies.
> Or have I misunderstood?

sfc is multi queue/channel, but has a single NAPI instance ?

Sounds wierd.

Please explain me, how GRO can be efficient.

I believe you have one napi per channel.



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