On Sun, 23 Aug 2020 17:08:30 +0300
Shay Agroskin <shayagr@xxxxxxxxxx> wrote:
> > diff --git a/include/net/xdp.h b/include/net/xdp.h
> > index 3814fb631d52..42f439f9fcda 100644
> > --- a/include/net/xdp.h
> > +++ b/include/net/xdp.h
> > @@ -72,7 +72,8 @@ struct xdp_buff {
> > void *data_hard_start;
> > struct xdp_rxq_info *rxq;
> > struct xdp_txq_info *txq;
> > - u32 frame_sz; /* frame size to deduce
> > data_hard_end/reserved tailroom*/
> > + u32 frame_sz:31; /* frame size to deduce
> > data_hard_end/reserved tailroom*/
> > + u32 mb:1; /* xdp non-linear buffer */
> > };
> >
> > /* Reserve memory area at end-of data area.
> > @@ -96,7 +97,8 @@ struct xdp_frame {
> > u16 len;
> > u16 headroom;
> > u32 metasize:8;
> > - u32 frame_sz:24;
> > + u32 frame_sz:23;
> > + u32 mb:1; /* xdp non-linear frame */
>
> Although this issue wasn't introduced with this patch, why not
> make frame_sz field to be the same size in xdp_buff and xdp_frame
> ?
This is all about struct layout and saving memory size, due to
cacheline access. Please read up on this and use the tool pahole to
inspect the struct memory layout.
--
Best regards,
Jesper Dangaard Brouer
MSc.CS, Principal Kernel Engineer at Red Hat
LinkedIn: http://www.linkedin.com/in/brouer
