netdev - Re: [PATCH net 2/2] ibmvnic: drop bad optimization in reuse_tx

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Date:   Wed, 01 Dec 2021 10:13:10 -0800
From:   Dany Madden <drt@...ux.ibm.com>
To:     Sukadev Bhattiprolu <sukadev@...ux.ibm.com>
Cc:     netdev@...r.kernel.org, Brian King <brking@...ux.ibm.com>,
        Rick Lindsley <ricklind@...ux.ibm.com>
Subject: Re: [PATCH net 2/2] ibmvnic: drop bad optimization in
 reuse_tx_pools()

On 2021-11-30 21:48, Sukadev Bhattiprolu wrote:
> When trying to decide whether or not reuse existing rx/tx pools
> we tried to allow a range of values for the pool parameters rather
> than exact matches. This was intended to reuse the resources for
> instance when switching between two VIO servers with different
> default parameters.
> 
> But this optimization is incomplete and breaks when we try to
> change the number of queues for instance. The optimization needs
> to be updated, so drop it for now and simplify the code.
> 
> Fixes: bbd809305bc7 ("ibmvnic: Reuse tx pools when possible")
> Reported-by: Dany Madden <drt@...ux.ibm.com>
> Signed-off-by: Sukadev Bhattiprolu <sukadev@...ux.ibm.com>
Reviewed-by: Dany Madden <drt@...ux.ibm.com>

> ---
>  drivers/net/ethernet/ibm/ibmvnic.c | 14 +++-----------
>  1 file changed, 3 insertions(+), 11 deletions(-)
> 
> diff --git a/drivers/net/ethernet/ibm/ibmvnic.c
> b/drivers/net/ethernet/ibm/ibmvnic.c
> index 6df92a872f0f..0bb3911dd014 100644
> --- a/drivers/net/ethernet/ibm/ibmvnic.c
> +++ b/drivers/net/ethernet/ibm/ibmvnic.c
> @@ -866,17 +866,9 @@ static bool reuse_tx_pools(struct ibmvnic_adapter 
> *adapter)
>  	old_mtu = adapter->prev_mtu;
>  	new_mtu = adapter->req_mtu;
> 
> -	/* Require MTU to be exactly same to reuse pools for now */
> -	if (old_mtu != new_mtu)
> -		return false;
> -
> -	if (old_num_pools == new_num_pools && old_pool_size == new_pool_size)
> -		return true;
> -
> -	if (old_num_pools < adapter->min_tx_queues ||
> -	    old_num_pools > adapter->max_tx_queues ||
> -	    old_pool_size < adapter->min_tx_entries_per_subcrq ||
> -	    old_pool_size > adapter->max_tx_entries_per_subcrq)
> +	if (old_mtu != new_mtu ||
> +	    old_num_pools != new_num_pools ||
> +	    old_pool_size != new_pool_size)
>  		return false;
> 
>  	return true;