linux-kernel - Re: [PATCH 5.15 042/136] ice: xsk: Force rings to be sized to power of 2

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Date:   Mon, 29 Aug 2022 13:16:40 +0200
From:   Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
CC:     <linux-kernel@...r.kernel.org>, <stable@...r.kernel.org>,
        "Alexander Lobakin" <alexandr.lobakin@...el.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        "Sasha Levin" <sashal@...nel.org>
Subject: Re: [PATCH 5.15 042/136] ice: xsk: Force rings to be sized to power
 of 2

On Mon, Aug 29, 2022 at 12:58:29PM +0200, Greg Kroah-Hartman wrote:
> From: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
> 
> [ Upstream commit 296f13ff3854535009a185aaf8e3603266d39d94 ]
> 
> With the upcoming introduction of batching to XSK data path,
> performance wise it will be the best to have the ring descriptor count
> to be aligned to power of 2.
> 
> Check if ring sizes that user is going to attach the XSK socket fulfill
> the condition above. For Tx side, although check is being done against
> the Tx queue and in the end the socket will be attached to the XDP
> queue, it is fine since XDP queues get the ring->count setting from Tx
> queues.

Hi Greg,

We had multiple customers reporting that this change makes them unable to
use max ring size which is 8160 for this particular driver (which is not a
power of 2 obviously) so we are about to send a patch that will drop this
limitation.

To avoid the double work, can you please not proceed with this one?
The other two:
ice: xsk: prohibit usage of non-balanced queue id
ice: xsk: use Rx rings XDP ring when picking NAPI context

are valid and needed.

FWIW this was a part of -next patch set, so I suppose you picked this due
to some dependency?

Thanks,
Maciej

> 
> Suggested-by: Alexander Lobakin <alexandr.lobakin@...el.com>
> Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
> Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
> Reviewed-by: Alexander Lobakin <alexandr.lobakin@...el.com>
> Acked-by: Magnus Karlsson <magnus.karlsson@...el.com>
> Link: https://lore.kernel.org/bpf/20220125160446.78976-3-maciej.fijalkowski@intel.com
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>  drivers/net/ethernet/intel/ice/ice_xsk.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/drivers/net/ethernet/intel/ice/ice_xsk.c b/drivers/net/ethernet/intel/ice/ice_xsk.c
> index 5581747947e57..0348cc4265034 100644
> --- a/drivers/net/ethernet/intel/ice/ice_xsk.c
> +++ b/drivers/net/ethernet/intel/ice/ice_xsk.c
> @@ -321,6 +321,13 @@ int ice_xsk_pool_setup(struct ice_vsi *vsi, struct xsk_buff_pool *pool, u16 qid)
>  	bool if_running, pool_present = !!pool;
>  	int ret = 0, pool_failure = 0;
>  
> +	if (!is_power_of_2(vsi->rx_rings[qid]->count) ||
> +	    !is_power_of_2(vsi->tx_rings[qid]->count)) {
> +		netdev_err(vsi->netdev, "Please align ring sizes to power of 2\n");
> +		pool_failure = -EINVAL;
> +		goto failure;
> +	}
> +
>  	if_running = netif_running(vsi->netdev) && ice_is_xdp_ena_vsi(vsi);
>  
>  	if (if_running) {
> @@ -343,6 +350,7 @@ int ice_xsk_pool_setup(struct ice_vsi *vsi, struct xsk_buff_pool *pool, u16 qid)
>  			netdev_err(vsi->netdev, "ice_qp_ena error = %d\n", ret);
>  	}
>  
> +failure:
>  	if (pool_failure) {
>  		netdev_err(vsi->netdev, "Could not %sable buffer pool, error = %d\n",
>  			   pool_present ? "en" : "dis", pool_failure);
> -- 
> 2.35.1
> 
> 
>