netdev - Re: [PATCH net] net/dim: Update DIM start sample after each DIM iteration

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Date:   Thu, 22 Nov 2018 11:37:42 -0800 (PST)
From:   David Miller <davem@...emloft.net>
To:     talgi@...lanox.com
Cc:     netdev@...r.kernel.org, tariqt@...lanox.com, saeedm@...lanox.com,
        f.fainelli@...il.com, andrew.gospodarek@...adcom.com
Subject: Re: [PATCH net] net/dim: Update DIM start sample after each DIM
 iteration

From: Tal Gilboa <talgi@...lanox.com>
Date: Wed, 21 Nov 2018 16:28:23 +0200

> On every iteration of net_dim, the algorithm may choose to
> check for the system state by comparing current data sample
> with previous data sample. After each of these comparison,
> regardless of the action taken, the sample used as baseline
> is needed to be updated.
> 
> This patch fixes a bug that causes DIM to take wrong decisions,
> due to never updating the baseline sample for comparison between
> iterations. This way, DIM always compares current sample with
> zeros.
> 
> Although this is a functional fix, it also improves and stabilizes
> performance as the algorithm works properly now.
> 
> Performance:
> Tested single UDP TX stream with pktgen:
> samples/pktgen/pktgen_sample03_burst_single_flow.sh -i p4p2 -d 1.1.1.1
> -m 24:8a:07:88:26:8b -f 3 -b 128
> 
> ConnectX-5 100GbE packet rate improved from 15-19Mpps to 19-20Mpps.
> Also, toggling between profiles is less frequent with the fix.
> 
> Fixes: 8115b750dbcb ("net/dim: use struct net_dim_sample as arg to net_dim")
> Signed-off-by: Tal Gilboa <talgi@...lanox.com>
> Reviewed-by: Tariq Toukan <tariqt@...lanox.com>

Applied and queued up for -stable.