netdev - Re: [PATCH net-next v2 1/2] selftests: drv-net: rss

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Message-ID: <20250902090345.GV15473@horms.kernel.org>
Date: Tue, 2 Sep 2025 10:03:45 +0100
From: Simon Horman <horms@...nel.org>
To: Jakub Kicinski <kuba@...nel.org>
Cc: davem@...emloft.net, netdev@...r.kernel.org, edumazet@...gle.com,
	pabeni@...hat.com, andrew+netdev@...n.ch, ecree.xilinx@...il.com,
	gal@...dia.com, joe@...a.to, linux-kselftest@...r.kernel.org,
	shuah@...nel.org
Subject: Re: [PATCH net-next v2 1/2] selftests: drv-net: rss_ctx: use Netlink
 for timed reconfig

On Mon, Sep 01, 2025 at 10:31:38AM -0700, Jakub Kicinski wrote:
> The rss_ctx test has gotten pretty flaky after I increased
> the queue count in NIPA 2->3. Not 100% clear why. We get
> a lot of failures in the rss_ctx.test_hitless_key_update case.
> 
> Looking closer it appears that the failures are mostly due
> to startup costs. I measured the following timing for ethtool -X:
>  - python cmd(shell=True)  : 150-250msec
>  - python cmd(shell=False) :  50- 70msec
>  - timed in bash           :  45- 55msec
>  - YNL Netlink call        :   2-  4msec
>  - .set_rxfh callback      :   1-  2msec
> 
> The target in the test was set to 200msec. We were mostly measuring
> ethtool startup cost it seems. Switch to YNL since it's 100x faster.
> 
> Lower the pass criteria to 150msec, no real science behind this number
> but we removed some overhead, drivers which previously passed 200msec
> should easily pass 150msec now.
> 
> Separately we should probably follow up on defaulting to shell=False,
> when script doesn't explicitly ask for True, because the overhead
> is rather significant.
> 
> Switch from _rss_key_rand() to random.randbytes(), YNL takes a binary
> array rather than array of ints.
> 
> Signed-off-by: Jakub Kicinski <kuba@...nel.org>
> ---
> v2:
>  - increase the threshold to safer 150msec
>  - mention change away from _rss_key_rand()
> v1: https://lore.kernel.org/20250829220712.327920-1-kuba@kernel.org

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