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

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Message-ID: <481149de-1212-4a43-a7cb-52351a0e29ad@linux.dev>
Date: Tue, 6 Aug 2024 23:59:01 +0800
From: Zhu Yanjun <yanjun.zhu@...ux.dev>
To: longli@...rosoft.com, "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>,
 Simon Horman <horms@...nel.org>, 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
Cc: stable@...r.kernel.org
Subject: Re: [PATCH net] net: mana: Fix doorbell out of order violation and
 avoid unnecessary doorbell rings

在 2024/8/6 7:38, longli@...uxonhyperv.com 写道:
> From: Long Li <longli@...rosoft.com>
> 
> After napi_complete_done() is called, another NAPI may be running on
> another CPU and ring the doorbell before the current CPU does. When
> combined with unnecessary rings when there is no need to ARM the CQ, this
> triggers error paths in the hardware.
> 
> Fix this by always ring the doorbell in sequence and avoid unnecessary
> rings.

Trivial problem^_^

s/ring/ringing ?

Zhu Yanjun

> 
> Cc: stable@...r.kernel.org
> Fixes: e1b5683ff62e ("net: mana: Move NAPI from EQ to CQ")
> Signed-off-by: Long Li <longli@...rosoft.com>
> ---
>   drivers/net/ethernet/microsoft/mana/mana_en.c | 24 ++++++++++++-------
>   include/net/mana/mana.h                       |  1 +
>   2 files changed, 16 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/net/ethernet/microsoft/mana/mana_en.c b/drivers/net/ethernet/microsoft/mana/mana_en.c
> index d2f07e179e86..7d08e23c6749 100644
> --- a/drivers/net/ethernet/microsoft/mana/mana_en.c
> +++ b/drivers/net/ethernet/microsoft/mana/mana_en.c
> @@ -1788,7 +1788,6 @@ static void mana_poll_rx_cq(struct mana_cq *cq)
>   static int mana_cq_handler(void *context, struct gdma_queue *gdma_queue)
>   {
>   	struct mana_cq *cq = context;
> -	u8 arm_bit;
>   	int w;
>   
>   	WARN_ON_ONCE(cq->gdma_cq != gdma_queue);
> @@ -1799,16 +1798,23 @@ static int mana_cq_handler(void *context, struct gdma_queue *gdma_queue)
>   		mana_poll_tx_cq(cq);
>   
>   	w = cq->work_done;
> -
> -	if (w < cq->budget &&
> -	    napi_complete_done(&cq->napi, w)) {
> -		arm_bit = SET_ARM_BIT;
> -	} else {
> -		arm_bit = 0;
> +	cq->work_done_since_doorbell += w;
> +
> +	if (w < cq->budget) {
> +		mana_gd_ring_cq(gdma_queue, SET_ARM_BIT);
> +		cq->work_done_since_doorbell = 0;
> +		napi_complete_done(&cq->napi, w);
> +	} else if (cq->work_done_since_doorbell >
> +		   cq->gdma_cq->queue_size / COMP_ENTRY_SIZE * 4) {
> +		/* MANA hardware requires at least one doorbell ring every 8
> +		 * wraparounds of CQ even there is no need to ARM. This driver
> +		 * rings the doorbell as soon as we have execceded 4
> +		 * wraparounds.
> +		 */
> +		mana_gd_ring_cq(gdma_queue, 0);
> +		cq->work_done_since_doorbell = 0;
>   	}
>   
> -	mana_gd_ring_cq(gdma_queue, arm_bit);
> -
>   	return w;
>   }
>   
> diff --git a/include/net/mana/mana.h b/include/net/mana/mana.h
> index 6439fd8b437b..7caa334f4888 100644
> --- a/include/net/mana/mana.h
> +++ b/include/net/mana/mana.h
> @@ -275,6 +275,7 @@ struct mana_cq {
>   	/* NAPI data */
>   	struct napi_struct napi;
>   	int work_done;
> +	int work_done_since_doorbell;
>   	int budget;
>   };
>