netdev - Re: [PATCH net-next v2 9/9] ibmvnic: Do not replenish RX buffers after every polling loop

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Message-ID: <1a4e7b1ef1fb101cbb26fb9d5867ee46@linux.vnet.ibm.com>
Date:   Thu, 19 Nov 2020 03:43:31 -0600
From:   ljp <ljp@...ux.vnet.ibm.com>
To:     Thomas Falcon <tlfalcon@...ux.ibm.com>
Cc:     kuba@...nel.org, cforno12@...ux.ibm.com, netdev@...r.kernel.org,
        ricklind@...ux.ibm.com, dnbanerg@...ibm.com,
        drt@...ux.vnet.ibm.com, brking@...ux.vnet.ibm.com,
        sukadev@...ux.vnet.ibm.com, linuxppc-dev@...ts.ozlabs.org,
        Linuxppc-dev 
        <linuxppc-dev-bounces+ljp=linux.ibm.com@...ts.ozlabs.org>
Subject: Re: [PATCH net-next v2 9/9] ibmvnic: Do not replenish RX buffers
 after every polling loop

On 2020-11-18 19:12, Thomas Falcon wrote:
> From: "Dwip N. Banerjee" <dnbanerg@...ibm.com>
> 
> Reduce the amount of time spent replenishing RX buffers by
> only doing so once available buffers has fallen under a certain
> threshold, in this case half of the total number of buffers, or
> if the polling loop exits before the packets processed is less
> than its budget.
> 
> Signed-off-by: Dwip N. Banerjee <dnbanerg@...ibm.com>
> ---
>  drivers/net/ethernet/ibm/ibmvnic.c | 5 ++++-
>  1 file changed, 4 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/ibm/ibmvnic.c
> b/drivers/net/ethernet/ibm/ibmvnic.c
> index 96df6d8fa277..9fe43ab0496d 100644
> --- a/drivers/net/ethernet/ibm/ibmvnic.c
> +++ b/drivers/net/ethernet/ibm/ibmvnic.c
> @@ -2537,7 +2537,10 @@ static int ibmvnic_poll(struct napi_struct
> *napi, int budget)
>  		frames_processed++;
>  	}
> 
> -	if (adapter->state != VNIC_CLOSING)
> +	if (adapter->state != VNIC_CLOSING &&
> +	    ((atomic_read(&adapter->rx_pool[scrq_num].available) <
> +	      adapter->req_rx_add_entries_per_subcrq / 2) ||
> +	      frames_processed < budget))

1/2 seems a simple and good algorithm.
Explaining why "frames_process < budget" is necessary in the commit 
message
or source code also helps.


>  		replenish_rx_pool(adapter, &adapter->rx_pool[scrq_num]);
>  	if (frames_processed < budget) {
>  		if (napi_complete_done(napi, frames_processed)) {