netdev - Re: [PATCH bpf-next v4 2/8] ice: xsk: force rings to be sized to power of 2

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Date:   Tue, 25 Jan 2022 12:28:52 +0100
From:   Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To:     Alexander Lobakin <alexandr.lobakin@...el.com>
Cc:     bpf@...r.kernel.org, ast@...nel.org, daniel@...earbox.net,
        netdev@...r.kernel.org, magnus.karlsson@...el.com
Subject: Re: [PATCH bpf-next v4 2/8] ice: xsk: force rings to be sized to
 power of 2

On Tue, Jan 25, 2022 at 12:23:06PM +0100, Alexander Lobakin wrote:
> From: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
> Date: Mon, 24 Jan 2022 17:55:41 +0100
> 
> > 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 rings 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.
> > 
> > Suggested-by: Alexander Lobakin <alexandr.lobakin@...el.com>
> > Signed-off-by: Maciej Fijalkowski <maciej.fijalkowski@...el.com>
> > ---
> >  drivers/net/ethernet/intel/ice/ice_xsk.c | 9 +++++++++
> >  1 file changed, 9 insertions(+)
> > 
> > diff --git a/drivers/net/ethernet/intel/ice/ice_xsk.c b/drivers/net/ethernet/intel/ice/ice_xsk.c
> > index 2388837d6d6c..0350f9c22c62 100644
> > --- a/drivers/net/ethernet/intel/ice/ice_xsk.c
> > +++ b/drivers/net/ethernet/intel/ice/ice_xsk.c
> > @@ -327,6 +327,14 @@ 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 at idx %d to power of 2\n", qid);
> 
> Ideally I'd pass xdp->extack from ice_xdp() to print this message
> directly in userspace (note that NL_SET_ERR_MSG{,_MOD}() don't
> support string formatting, but the user already knows QID at this
> point).

I thought about that as well but it seemed to me kinda off to have a
single extack usage in here. Updating the rest of error paths in
ice_xsk_pool_setup() to make use of extack is a candidate for a separate
patch to me.

WDYT?

> 
> > +		pool_failure = -EINVAL;
> > +		goto failure;
> > +	}
> > +
> >  	if_running = netif_running(vsi->netdev) && ice_is_xdp_ena_vsi(vsi);
> >  
> >  	if (if_running) {
> > @@ -349,6 +357,7 @@ 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);
> > -- 
> > 2.33.1
> 
> Thanks,
> Al