linux-kernel - Re: [PATCH v2 net] net: mana: Fix doorbell out of order violation and avoid unnecessary doorbell rings

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Message-ID: <20240809084716.GA3432921@kernel.org>
Date: Fri, 9 Aug 2024 09:47:16 +0100
From: Simon Horman <horms@...nel.org>
To: longli@...rosoft.com
Cc: "K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Shradha Gupta <shradhagupta@...ux.microsoft.com>,
	Konstantin Taranov <kotaranov@...rosoft.com>,
	Souradeep Chakrabarti <schakrabarti@...ux.microsoft.com>,
	Erick Archer <erick.archer@...look.com>,
	linux-hyperv@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [PATCH v2 net] net: mana: Fix doorbell out of order violation
 and avoid unnecessary doorbell rings

On Wed, Aug 07, 2024 at 04:17:06PM -0700, longli@...uxonhyperv.com wrote:
> From: Long Li <longli@...rosoft.com>
> 
> After napi_complete_done() is called when NAPI is polling in the current
> process context, another NAPI may be scheduled and start running in
> softirq on another CPU and may ring the doorbell before the current CPU
> does. When combined with unnecessary rings when there is no need to arm
> the CQ, it triggers error paths in the hardware.
> 
> This patch fixes this by calling napi_complete_done() after doorbell
> rings. It limits the number of unnecessary rings when there is
> no need to arm. MANA hardware specifies that there must be one doorbell
> ring every 8 CQ wraparounds. This driver guarantees one doorbell ring as
> soon as the number of consumed CQEs exceeds 4 CQ wraparounds. In pratical

nit: practical

     Flagged by checkpatch.pl --codespell

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