netdev - Re: [PATCH bpf-next] xdp: report rx queue index in xdp

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Date:   Wed, 17 Aug 2022 14:35:53 +0200
From:   Lorenzo Bianconi <lorenzo@...nel.org>
To:     Jesper Dangaard Brouer <jbrouer@...hat.com>
Cc:     bpf@...r.kernel.org, brouer@...hat.com, ast@...nel.org,
        daniel@...earbox.net, andrii@...nel.org, netdev@...r.kernel.org,
        davem@...emloft.net, kuba@...nel.org, edumazet@...gle.com,
        pabeni@...hat.com, hawk@...nel.org, john.fastabend@...il.com,
        lorenzo.bianconi@...hat.com
Subject: Re: [PATCH bpf-next] xdp: report rx queue index in xdp_frame

> 
> On 25/07/2022 12.56, Lorenzo Bianconi wrote:
> > Report rx queue index in xdp_frame according to the xdp_buff xdp_rxq_info
> > pointer. xdp_frame queue_index is currently used in cpumap code to covert
> > the xdp_frame into a xdp_buff.
> 
> Hmm, I'm unsure about this change, because the XDP-hints will also
> contain the rx_queue number.

ack, but in this way each driver needs to fill this info, right? Maybe we can
keep rx_queue number here and remove it from XDP-hints metadata?

> 
> I do think it is relevant for the BPF-prog to get access to the rx_queue
> index, because it can be used for scaling the workload.
> 
> > xdp_frame size is not increased adding queue_index since an alignment padding
> > in the structure is used to insert queue_index field.
> 
> The rx_queue could be reduced from u32 to u16, but it might be faster to
> keep it u32, and reduce it when others need the space.

ack, agree.

Regards,
Lorenzo

> 
> > Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
> > ---
> >   include/net/xdp.h   | 2 ++
> >   kernel/bpf/cpumap.c | 2 +-
> >   2 files changed, 3 insertions(+), 1 deletion(-)
> > 
> > diff --git a/include/net/xdp.h b/include/net/xdp.h
> > index 04c852c7a77f..3567866b0af5 100644
> > --- a/include/net/xdp.h
> > +++ b/include/net/xdp.h
> > @@ -172,6 +172,7 @@ struct xdp_frame {
> >   	struct xdp_mem_info mem;
> >   	struct net_device *dev_rx; /* used by cpumap */
> >   	u32 flags; /* supported values defined in xdp_buff_flags */
> > +	u32 queue_index;
> >   };
> >   static __always_inline bool xdp_frame_has_frags(struct xdp_frame *frame)
> > @@ -301,6 +302,7 @@ struct xdp_frame *xdp_convert_buff_to_frame(struct xdp_buff *xdp)
> >   	/* rxq only valid until napi_schedule ends, convert to xdp_mem_info */
> >   	xdp_frame->mem = xdp->rxq->mem;
> > +	xdp_frame->queue_index = xdp->rxq->queue_index;
> >   	return xdp_frame;
> >   }
> > diff --git a/kernel/bpf/cpumap.c b/kernel/bpf/cpumap.c
> > index f4860ac756cd..09a792d088b3 100644
> > --- a/kernel/bpf/cpumap.c
> > +++ b/kernel/bpf/cpumap.c
> > @@ -228,7 +228,7 @@ static int cpu_map_bpf_prog_run_xdp(struct bpf_cpu_map_entry *rcpu,
> >   		rxq.dev = xdpf->dev_rx;
> >   		rxq.mem = xdpf->mem;
> > -		/* TODO: report queue_index to xdp_rxq_info */
> > +		rxq.queue_index = xdpf->queue_index;
> >   		xdp_convert_frame_to_buff(xdpf, &xdp);
> 

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