Re: [Xen-devel] [PATCH net-next v3 2/2] xen-netback: Grant copy the header instead of map and memcpy

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2014-04-03 at 09:07 +0100, Paul Durrant wrote:
> > -----Original Message-----
> > From: Zoltan Kiss
> > Sent: 02 April 2014 18:05
> > To: Ian Campbell; Wei Liu; xen-devel@xxxxxxxxxxxxxxxxxxxx
> > Cc: Paul Durrant; netdev@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> > Jonathan Davies; Zoltan Kiss
> > Subject: [PATCH net-next v3 2/2] xen-netback: Grant copy the header
> > instead of map and memcpy
> > 
> > An old inefficiency of the TX path that we are grant mapping the first slot,
> > and then copy the header part to the linear area. Instead, doing a grant 
> > copy
> > for that header straight on is more reasonable. Especially because there are
> > ongoing efforts to make Xen avoiding TLB flush after unmap when the page
> > were
> > not touched in Dom0. In the original way the memcpy ruined that.
> > The key changes:
> > - the vif has a tx_copy_ops array again
> > - xenvif_tx_build_gops sets up the grant copy operations
> > - we don't have to figure out whether the header and first frag are on the
> > same
> >   grant mapped page or not
> > Note, we only grant copy PKT_PROT_LEN bytes from the first slot, the rest 
> > (if
> > any) will be on the first frag, which is grant mapped. If the first slot is
> > smaller than PKT_PROT_LEN, then we grant copy that, and later
> > __pskb_pull_tail
> > will pull more from the frags (if any)
> > 
> > Signed-off-by: Zoltan Kiss <zoltan.kiss@xxxxxxxxxx>
> 
> Looks good to me.
> 
> Reviewed-by: Paul Durrant <paul.durrant@xxxxxxxxxx>

Me too:

Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>




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