netdev - Re: [PATCH net-next 1/4] net: xdp: introduce bulking for xdp tx return path

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Date:   Wed, 28 Oct 2020 11:23:04 +0100
From:   Lorenzo Bianconi <lorenzo@...nel.org>
To:     Ilias Apalodimas <ilias.apalodimas@...aro.org>
Cc:     netdev@...r.kernel.org, bpf@...r.kernel.org,
        lorenzo.bianconi@...hat.com, davem@...emloft.net, kuba@...nel.org,
        brouer@...hat.com
Subject: Re: [PATCH net-next 1/4] net: xdp: introduce bulking for xdp tx
 return path

> Hi Lorenzo,

Hi Ilias,

thx for the review.

> 
> On Tue, Oct 27, 2020 at 08:04:07PM +0100, Lorenzo Bianconi wrote:

[...]

> > +void xdp_return_frame_bulk(struct xdp_frame *xdpf,
> > +			   struct xdp_frame_bulk *bq)
> > +{
> > +	struct xdp_mem_info *mem = &xdpf->mem;
> > +	struct xdp_mem_allocator *xa, *nxa;
> > +
> > +	if (mem->type != MEM_TYPE_PAGE_POOL) {
> > +		__xdp_return(xdpf->data, &xdpf->mem, false);
> > +		return;
> > +	}
> > +
> > +	rcu_read_lock();
> > +
> > +	xa = bq->xa;
> > +	if (unlikely(!xa || mem->id != xa->mem.id)) {
> 
> Why is this marked as unlikely? The driver passes it as NULL. Should unlikely be
> checked on both xa and the comparison?

xa is NULL only for the first xdp_frame in the burst while it is set for
subsequent ones. Do you think it is better to remove it?

> 
> > +		nxa = rhashtable_lookup(mem_id_ht, &mem->id, mem_id_rht_params);
> 
> Is there a chance nxa can be NULL?

I do not think so since the page_pool is not destroyed while there are
in-flight pages, right?

Regards,
Lorenzo

> 
> > +		if (unlikely(!xa)) {
> 
> Same here, driver passes it as NULL
> 
> > +			bq->count = 0;
> > +			bq->xa = nxa;
> > +			xa = nxa;
> > +		}
> > +	}
> > +
> > +	if (mem->id != xa->mem.id || bq->count == XDP_BULK_QUEUE_SIZE)
> > +		xdp_flush_frame_bulk(bq);
> > +
> > +	bq->q[bq->count++] = xdpf->data;
> > +	if (mem->id != xa->mem.id)
> > +		bq->xa = nxa;
> > +
> > +	rcu_read_unlock();
> > +}
> > +EXPORT_SYMBOL_GPL(xdp_return_frame_bulk);
> > +
> >  void xdp_return_buff(struct xdp_buff *xdp)
> >  {
> >  	__xdp_return(xdp->data, &xdp->rxq->mem, true);
> > -- 
> > 2.26.2
> > 
> 
> Cheers
> /Ilias

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