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

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Message-ID: <20201029140838.GA69963@apalos.home>
Date:   Thu, 29 Oct 2020 16:08:38 +0200
From:   Ilias Apalodimas <ilias.apalodimas@...aro.org>
To:     Lorenzo Bianconi <lorenzo.bianconi@...hat.com>
Cc:     Jesper Dangaard Brouer <brouer@...hat.com>,
        Lorenzo Bianconi <lorenzo@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, davem@...emloft.net, kuba@...nel.org
Subject: Re: [PATCH net-next 1/4] net: xdp: introduce bulking for xdp tx
 return path

On Thu, Oct 29, 2020 at 03:02:16PM +0100, Lorenzo Bianconi wrote:
> > On Tue, 27 Oct 2020 20:04:07 +0100
> > Lorenzo Bianconi <lorenzo@...nel.org> wrote:
> > 
> > > diff --git a/net/core/xdp.c b/net/core/xdp.c
> > > index 48aba933a5a8..93eabd789246 100644
> > > --- a/net/core/xdp.c
> > > +++ b/net/core/xdp.c
> > > @@ -380,6 +380,57 @@ void xdp_return_frame_rx_napi(struct xdp_frame *xdpf)
> > >  }
> > >  EXPORT_SYMBOL_GPL(xdp_return_frame_rx_napi);
> > >  
> > > +void xdp_flush_frame_bulk(struct xdp_frame_bulk *bq)
> > > +{
> > > +	struct xdp_mem_allocator *xa = bq->xa;
> > > +	int i;
> > > +
> > > +	if (unlikely(!xa))
> > > +		return;
> > > +
> > > +	for (i = 0; i < bq->count; i++) {
> > > +		struct page *page = virt_to_head_page(bq->q[i]);
> > > +
> > > +		page_pool_put_full_page(xa->page_pool, page, false);
> > > +	}
> > > +	bq->count = 0;
> > > +}
> > > +EXPORT_SYMBOL_GPL(xdp_flush_frame_bulk);
> > > +
> > > +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)) {
> > > +		nxa = rhashtable_lookup(mem_id_ht, &mem->id, mem_id_rht_params);
> > > +		if (unlikely(!xa)) {
> > > +			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);
> > 
> > We (Ilias my co-maintainer and I) think above code is hard to read and
> > understand (as a reader you need to keep too many cases in your head).
> > 
> > I think we both have proposals to improve this, here is mine:
> > 
> > /* Defers return when frame belongs to same mem.id as previous frame */
> > 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;
> > 
> >         if (mem->type != MEM_TYPE_PAGE_POOL) {
> >                 __xdp_return(xdpf->data, &xdpf->mem, false);
> >                 return;
> >         }
> > 
> >         rcu_read_lock();
> > 
> >         xa = bq->xa;
> >         if (unlikely(!xa)) {
> > 		xa = rhashtable_lookup(mem_id_ht, &mem->id, mem_id_rht_params);
> >                 bq->count = 0;
> >                 bq->xa = xa;
> >         }
> > 
> >         if (bq->count == XDP_BULK_QUEUE_SIZE)
> >                 xdp_flush_frame_bulk(bq);
> > 
> >         if (mem->id != xa->mem.id) {
> > 		xdp_flush_frame_bulk(bq);
> > 		bq->xa = rhashtable_lookup(mem_id_ht, &mem->id, mem_id_rht_params);
> >         }
> > 
> > 	bq->q[bq->count++] = xdpf->data;
> > 
> >         rcu_read_unlock();
> > }
> > 
> > Please review for correctness, and also for readability.
> 
> the code seems fine to me (and even easier to read :)).
> I will update v2 using this approach. Thx.
+1 this is close to what we discussed this morning and it detangles 1 more 'weird' 
if case 


Thanks
/Ilias
> 
> Regards,
> Lorenzo
> 
> > 
> > -- 
> > Best regards,
> >   Jesper Dangaard Brouer
> >   MSc.CS, Principal Kernel Engineer at Red Hat
> >   LinkedIn: http://www.linkedin.com/in/brouer
> >