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

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Message-ID: <20121003094732.GQ29125@suse.de>
Date:	Wed, 3 Oct 2012 10:47:32 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Rick Jones <rick.jones2@...com>
Cc:	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 Tue, Oct 02, 2012 at 03:48:57PM -0700, Rick Jones wrote:
> On 10/02/2012 01:45 AM, Mel Gorman wrote:
> 
> >SIZE=64
> >taskset -c 0 netserver
> >taskset -c 1 netperf -t UDP_STREAM -i 50,6 -I 99,1 -l 20 -H 127.0.0.1 -- -P 15895 -s 32768 -S 32768 -m $SIZE -M $SIZE
> 
> Just FYI, unless you are running a hacked version of netperf, the
> "50" in "-i 50,6" will be silently truncated to 30.
> 

I'm not using a hacked version of netperf. The 50,6 has been there a long
time so I'm not sure where I took it from any more. It might have been an
older version or me being over-zealous at the time.

> 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.

Thanks!

-- 
Mel Gorman
SUSE Labs
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