From mboxrd@z Thu Jan 1 00:00:00 1970 From: Edward Cree Subject: Re: [RFC PATCH] udp: allow busy_poll on some unconnected sockets Date: Thu, 10 Apr 2014 19:38:24 +0100 Message-ID: <5346E520.7080007@solarflare.com> References: <53455581.7060209@solarflare.com> <20140409145129.GA4002@sbohrermbp13-local.rgmadvisors.com> <53457334.1030602@solarflare.com> <1397154745.16584.42.camel@edumazet-glaptop2.roam.corp.google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Cc: , Shawn Bohrer , "Shawn Bohrer" , Jonathan Cooper To: Eric Dumazet Return-path: Received: from webmail.solarflare.com ([12.187.104.25]:16852 "EHLO webmail.solarflare.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S965159AbaDJSi2 (ORCPT ); Thu, 10 Apr 2014 14:38:28 -0400 In-Reply-To: <1397154745.16584.42.camel@edumazet-glaptop2.roam.corp.google.com> Sender: netdev-owner@vger.kernel.org List-ID: 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? (Note that it doesn't matter if there are other NAPI-using devices on the host, since the socket is bound to a local address and thus is only going to receive packets from the one device that has that address. So maybe IFF_SINGLE_NAPI is a bad name and it should be IFF_DEVICE_ONLY_HAS_A_SINGLE_NAPI_CONTEXT. But that's a bit unwieldy ;)