[Intel-wired-lan] [PATCH v2 net-next 2/9] xdp: initialize xdp_buff mb bit to 0 in all XDP drivers

[Intel-wired-lan] [PATCH v2 net-next 2/9] xdp: initialize xdp_buff mb bit to 0 in all XDP drivers

[Jesper Dangaard Brouer]

On Thu,  3 Sep 2020 22:58:46 +0200
Lorenzo Bianconi <lorenzo@kernel.org> wrote:

> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> index 0b675c34ce49..20c8fd3cd4a3 100644
> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> @@ -2298,6 +2298,7 @@ static int ixgbe_clean_rx_irq(struct ixgbe_q_vector *q_vector,
>  #if (PAGE_SIZE < 8192)
>  	xdp.frame_sz = ixgbe_rx_frame_truesize(rx_ring, 0);
>  #endif
> +	xdp.mb = 0;
>  
>  	while (likely(total_rx_packets < budget)) {
>  		union ixgbe_adv_rx_desc *rx_desc;

In this ixgbe driver you are smart and init the xdp.mb bit outside the
(like xdp.frame_sz, when frame_sz is constant).   This is a nice
optimization, but the driver developer that adds XDP multi-buffer
support must remember to reset it.  The patch itself is okay, it is
just something to keep in-mind when reviewing/changing drivers.

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

[Intel-wired-lan] [PATCH v2 net-next 2/9] xdp: initialize xdp_buff mb bit to 0 in all XDP drivers

[Lorenzo Bianconi]

> On Thu,  3 Sep 2020 22:58:46 +0200
> Lorenzo Bianconi <lorenzo@kernel.org> wrote:
> 
> > diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> > index 0b675c34ce49..20c8fd3cd4a3 100644
> > --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> > +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
> > @@ -2298,6 +2298,7 @@ static int ixgbe_clean_rx_irq(struct ixgbe_q_vector *q_vector,
> >  #if (PAGE_SIZE < 8192)
> >  	xdp.frame_sz = ixgbe_rx_frame_truesize(rx_ring, 0);
> >  #endif
> > +	xdp.mb = 0;
> >  
> >  	while (likely(total_rx_packets < budget)) {
> >  		union ixgbe_adv_rx_desc *rx_desc;
> 
> In this ixgbe driver you are smart and init the xdp.mb bit outside the
> (like xdp.frame_sz, when frame_sz is constant).   This is a nice
> optimization, but the driver developer that adds XDP multi-buffer
> support must remember to reset it.  The patch itself is okay, it is
> just something to keep in-mind when reviewing/changing drivers.

yes, I have just decided to avoid unnecessary instructions for the moment.

Regards,
Lorenzo

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