linux-kernel - Re: [LKP] [lkp] [sctp] a6c2f79287: netperf.Throughput

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Date:	Wed, 17 Aug 2016 15:53:57 +0800
From:	Aaron Lu <aaron.lu@...el.com>
To:	Xin Long <lucien.xin@...il.com>
Cc:	kernel test robot <xiaolong.ye@...el.com>,
	Stephen Rothwell <sfr@...b.auug.org.au>, lkp@...org,
	"David S. Miller" <davem@...emloft.net>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [LKP] [lkp] [sctp] a6c2f79287: netperf.Throughput_Mbps -37.2%
 regression

On Wed, Aug 17, 2016 at 03:42:34PM +0800, Aaron Lu wrote:
> On 08/17/2016 03:35 PM, Xin Long wrote:
> >>  include/net/sctp/structs.h | 3 +++
> >>  1 file changed, 3 insertions(+)
> >>
> >> diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
> >> index d8e464aacb20..932f2780d3a4 100644
> >> --- a/include/net/sctp/structs.h
> >> +++ b/include/net/sctp/structs.h
> >> @@ -602,6 +602,9 @@ struct sctp_chunk {
> >>         /* This needs to be recoverable for SCTP_SEND_FAILED events. */
> >>         struct sctp_sndrcvinfo sinfo;
> >>
> >> +       unsigned long prsctp_param;
> >> +       int sent_count;
> >> +
> >>         /* Which association does this belong to?  */
> >>         struct sctp_association *asoc;
> >>
> >> --
> >> 2.5.5
> >>
> >> Then the performance dropped to the same as the bisected commit
> >> a6c2f792873a:
> >> $ cat 4.7.0-rc6-01198-g98dd2532b14e/0/netperf.json
> >> {
> >>   "netperf.Throughput_Mbps": [
> >>    754.494375
> >>   ]
> >> }
> >>
> >> I think this agrees with the perf data in that the newly added function
> >> doesn't show up in the perf-profile but still, the performance drops.
> >> So the only possible reason is the newly added fields to the sctp_chunk
> >> structure.
> >>
> >> Is this expected?
> > interesting , you didn't include the modification of the functions
> > parts, right ?
> 
> Yes.
> 
> > you mean only this two line:
> >> +       unsigned long prsctp_param;
> >> +       int sent_count;ca;
> > 
> > caused the performance issue ?
>  
> Right.

Note the test is done on my own Sandybridge desktop, I'll queue a job to
run on the Ivybridge test box now.