netdev - Re: [PATCH iwl-net] ice: fix stats being updated by way too large values

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Date: Wed, 28 Feb 2024 10:12:18 +0000
From: Simon Horman <horms@...nel.org>
To: Przemek Kitszel <przemyslaw.kitszel@...el.com>
Cc: intel-wired-lan@...ts.osuosl.org, netdev@...r.kernel.org,
	Tony Nguyen <anthony.l.nguyen@...el.com>, lukasz.czapnik@...el.com,
	Jacob Keller <jacob.e.keller@...el.com>,
	Alexander Lobakin <aleksander.lobakin@...el.com>,
	Nebojsa Stevanovic <nebojsa.stevanovic@...re.com>,
	Christian Rohmann <christian.rohmann@...vex.de>
Subject: Re: [PATCH iwl-net] ice: fix stats being updated by way too large
 values

On Tue, Feb 27, 2024 at 03:31:06PM +0100, Przemek Kitszel wrote:
> Simplify stats accumulation logic to fix the case where we don't take
> previous stat value into account, we should always respect it.
> 
> Main netdev stats of our PF (Tx/Rx packets/bytes) were reported orders of
> magnitude too big during OpenStack reconfiguration events, possibly other
> reconfiguration cases too.
> 
> The regression was reported to be between 6.1 and 6.2, so I was almost
> certain that on of the two "preserve stats over reset" commits were the
> culprit. While reading the code, it was found that in some cases we will
> increase the stats by arbitrarily large number (thanks to ignoring "-prev"
> part of condition, after zeroing it).
> 
> Note that this fixes also the case where we were around limits of u64, but
> that was not the regression reported.
> 
> Full disclosure: I remember suggesting this particular piece of code to
> Ben a few years ago, so blame on me.
> 
> Fixes: 2fd5e433cd26 ("ice: Accumulate HW and Netdev statistics over reset")
> Reported-by: Nebojsa Stevanovic <nebojsa.stevanovic@...re.com>
> Link: https://lore.kernel.org/intel-wired-lan/VI1PR02MB439744DEDAA7B59B9A2833FE912EA@VI1PR02MB4397.eurprd02.prod.outlook.com
> Reported-by: Christian Rohmann <christian.rohmann@...vex.de>
> Link: https://lore.kernel.org/intel-wired-lan/f38a6ca4-af05-48b1-a3e6-17ef2054e525@inovex.de
> Reviewed-by: Jacob Keller <jacob.e.keller@...el.com>
> Signed-off-by: Przemek Kitszel <przemyslaw.kitszel@...el.com>

Reviewed-by: Simon Horman <horms@...nel.org>