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

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Date:	Thu, 18 Aug 2016 11:21:56 +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 Thu, Aug 18, 2016 at 02:06:50AM +0800, Xin Long wrote:
> >
> > It doesn't seem memory is an issue.
> >
> > The whole dump is about the same.
> > The MemFree and MemAvailable doesn't change much.
> >
> Hi, Aaron
> 
> 1)
> I talked with Marcelo about this one.
> He said it might be related with cacheline.  the  new field distroyed
> the prior cacheline. So on top of commit 826d253d57b1, pls only add
> +       unsigned long prsctp_param;
> 
> to the end of struct sctp_chunk, then try.

This doesn't work.
 
> 2)
> if 1) still doesn't work, I may think about to drop prsctp_param in
> sctp_chunk, and reuse msg->expire_at. as for sent_count, I will
> put it to the mem hole of sctp_chunk.
> 
> So pls also try the attachment patch,  on top of commit a6c2f792873a

Good news, this brings the performance back on my Sandybridge desktop :)
I have queued jobs to the Ivybridge test box but I guess the result is
the same, but will let you know if it isn't.

It looks like the size of the structure plays a role here, but not clear
to me what happened underneath. Do you know why?

Thanks,
Aaron

> 
> Thanks.

> diff --git a/include/net/sctp/structs.h b/include/net/sctp/structs.h
> index 6bcda71..008cb76 100644
> --- a/include/net/sctp/structs.h
> +++ b/include/net/sctp/structs.h
> @@ -524,7 +524,11 @@ struct sctp_datamsg {
>  	struct list_head chunks;
>  	/* Reference counting. */
>  	atomic_t refcnt;
> -	/* When is this message no longer interesting to the peer? */
> +	/* Re-use this field to record param for prsctp policies,
> +	 * for TTL policy, it is the time_to_drop of this chunk,
> +	 * for RTX policy, it is the max_sent_count of this chunk,
> +	 * for PRIO policy, it is the priority of this chunk.
> +	 */
>  	unsigned long expires_at;
>  	/* Did the messenge fail to send? */
>  	int send_error;
> @@ -553,6 +557,9 @@ struct sctp_chunk {
>  
>  	atomic_t refcnt;
>  
> +	/* How many times this chunk have been sent, for prsctp RTX policy */
> +	int sent_count;
> +
>  	/* This is our link to the per-transport transmitted list.  */
>  	struct list_head transmitted_list;
>  
> @@ -602,16 +609,6 @@ struct sctp_chunk {
>  	/* This needs to be recoverable for SCTP_SEND_FAILED events. */
>  	struct sctp_sndrcvinfo sinfo;
>  
> -	/* We use this field to record param for prsctp policies,
> -	 * for TTL policy, it is the time_to_drop of this chunk,
> -	 * for RTX policy, it is the max_sent_count of this chunk,
> -	 * for PRIO policy, it is the priority of this chunk.
> -	 */
> -	unsigned long prsctp_param;
> -
> -	/* How many times this chunk have been sent, for prsctp RTX policy */
> -	int sent_count;
> -
>  	/* Which association does this belong to?  */
>  	struct sctp_association *asoc;
>  
> diff --git a/net/sctp/chunk.c b/net/sctp/chunk.c
> index 2698d12..0c53d64 100644
> --- a/net/sctp/chunk.c
> +++ b/net/sctp/chunk.c
> @@ -349,7 +349,7 @@ int sctp_chunk_abandoned(struct sctp_chunk *chunk)
>  	}
>  
>  	if (SCTP_PR_TTL_ENABLED(chunk->sinfo.sinfo_flags) &&
> -	    time_after(jiffies, chunk->prsctp_param)) {
> +	    time_after(jiffies, chunk->msg->expires_at)) {
>  		if (chunk->sent_count)
>  			chunk->asoc->abandoned_sent[SCTP_PR_INDEX(TTL)]++;
>  		else
> diff --git a/net/sctp/sm_make_chunk.c b/net/sctp/sm_make_chunk.c
> index 2c431ee..c7110a9 100644
> --- a/net/sctp/sm_make_chunk.c
> +++ b/net/sctp/sm_make_chunk.c
> @@ -718,7 +718,7 @@ static void sctp_set_prsctp_policy(struct sctp_chunk *chunk,
>  		return;
>  
>  	if (SCTP_PR_TTL_ENABLED(sinfo->sinfo_flags))
> -		chunk->prsctp_param =
> +		chunk->msg->expires_at =
>  			jiffies + msecs_to_jiffies(sinfo->sinfo_timetolive);
>  }
>