netdev - Re: [PATCH net-next-2.6] ixgbe: fix multi-ring polling

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Date:	Tue, 16 Jun 2009 14:11:45 -0700 (Pacific Daylight Time)
From:	"Brandeburg, Jesse" <jesse.brandeburg@...el.com>
To:	Andy Gospodarek <andy@...yhouse.net>
cc:	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"Waskiewicz Jr, Peter P" <peter.p.waskiewicz.jr@...el.com>,
	"Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>
Subject: Re: [PATCH net-next-2.6] ixgbe: fix multi-ring polling



On Tue, 16 Jun 2009, Andy Gospodarek wrote:

> 
> When looking at ixgbe_clean_rxtx_many I noticed two small problems.
> 
>  - work_done needs to be cleared before calling ixgbe_clean_rx_irq since
>    it will exit without cleaning any buffers when work_done is greater
>    than budget (which could happen pretty often after the first ring is
>    cleaned).  A total count will ensure we still return the correct
>    number of frames processed.

but (not seen in the below patch) the budget is divided by the number of 
rings on this vector before it is passed to rx_clean, so each ring will 
always get a chance to clean at least one buffer.

>  - napi_complete should only be called if all rings associated with this
>    napi instance were cleaned completely.  It seems wise to stay on the
>    poll-list if not completely cleaned.

that part I agree to.

> 
> This has been compile tested only.

we can test it but I think we need a V2, see below...

> 
> Signed-off-by: Andy Gospodarek <andy@...yhouse.net>
> ---
> 
>  ixgbe_main.c |   11 +++++++----
>  1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/ixgbe/ixgbe_main.c b/drivers/net/ixgbe/ixgbe_main.c
> index a551a96..c009642 100644
> --- a/drivers/net/ixgbe/ixgbe_main.c
> +++ b/drivers/net/ixgbe/ixgbe_main.c
> @@ -1362,9 +1362,9 @@ static int ixgbe_clean_rxtx_many(struct napi_struct *napi, int budget)
>  	                       container_of(napi, struct ixgbe_q_vector, napi);
>  	struct ixgbe_adapter *adapter = q_vector->adapter;
>  	struct ixgbe_ring *ring = NULL;
> -	int work_done = 0, i;
> +	int work_done = 0, total_work = 0, i;
>  	long r_idx;
> -	bool tx_clean_complete = true;
> +	bool rx_clean_complete = true, tx_clean_complete = true;
>  
>  	r_idx = find_first_bit(q_vector->txr_idx, adapter->num_tx_queues);
>  	for (i = 0; i < q_vector->txr_count; i++) {
> @@ -1384,12 +1384,15 @@ static int ixgbe_clean_rxtx_many(struct napi_struct *napi, int budget)
>  	budget = max(budget, 1);
>  	r_idx = find_first_bit(q_vector->rxr_idx, adapter->num_rx_queues);
>  	for (i = 0; i < q_vector->rxr_count; i++) {
> +		work_done = 0;
>  		ring = &(adapter->rx_ring[r_idx]);
>  #ifdef CONFIG_IXGBE_DCA
>  		if (adapter->flags & IXGBE_FLAG_DCA_ENABLED)
>  			ixgbe_update_rx_dca(adapter, ring);
>  #endif
>  		ixgbe_clean_rx_irq(q_vector, ring, &work_done, budget);
> +		total_work += work_done;
> +		rx_clean_complete &= (work_done < budget);
>  		r_idx = find_next_bit(q_vector->rxr_idx, adapter->num_rx_queues,
>  		                      r_idx + 1);
>  	}
> @@ -1397,7 +1400,7 @@ static int ixgbe_clean_rxtx_many(struct napi_struct *napi, int budget)
>  	r_idx = find_first_bit(q_vector->rxr_idx, adapter->num_rx_queues);
>  	ring = &(adapter->rx_ring[r_idx]);
>  	/* If all Rx work done, exit the polling mode */
> -	if (work_done < budget) {
> +	if (rx_clean_complete && tx_clean_complete) {
>  		napi_complete(napi);
>  		if (adapter->itr_setting & 1)
>  			ixgbe_set_itr_msix(q_vector);
> @@ -1407,7 +1410,7 @@ static int ixgbe_clean_rxtx_many(struct napi_struct *napi, int budget)
>  		return 0;
>  	}
>  
> -	return work_done;
> +	return total_work;

I don't think you can return total_work here unless it is always
 == budget, otherwise NAPI will hang.

before the only values that would ever be returned were:
 
1) napi_complete, return work_done (work_done < budget)
2) return work_done (work_done >= budget)

I'm not sure if the > case is even valid in the new napi model, the only 
one we ever use is the work_done == budget to continue polling.

>  }
>  
>  /**
> 
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