linux-kernel - Re: Netperf UDP_STREAM regression due to not sending IPIs in ttwu

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Date:	Wed, 03 Oct 2012 12:22:11 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Mel Gorman <mgorman@...e.de>
Cc:	Rick Jones <rick.jones2@...com>, Mike Galbraith <efault@....de>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Netperf UDP_STREAM regression due to not sending IPIs in
 ttwu_queue()

On Wed, 2012-10-03 at 10:47 +0100, Mel Gorman wrote:
> On Tue, Oct 02, 2012 at 03:48:57PM -0700, Rick Jones wrote:

> > PS - I trust it is the receive-side throughput being reported/used
> > with UDP_STREAM :)
> 
> Good question. Now that I examine the scripts, it is in fact the sending
> side that is being reported which is flawed. Granted I'm not expecting any
> UDP loss on loopback and looking through a range of results, the
> difference is marginal. It's still wrong to report just the sending side
> for UDP_STREAM and I'll correct the scripts for it in the future.

You can have drops even on loopback if the receiver doesnt drain its
socket receive queue fast enough.



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