Re: [PATCH v2] net/virtio: cache Rx/Tx offload ability check

[Yuanhan Liu <yuanhan.liu@linux.intel.com>]

On Tue, Nov 08, 2016 at 09:43:14AM +0100, Olivier Matz wrote:
> Hi Yuanhan,
> 
> On 11/04/2016 03:29 PM, Yuanhan Liu wrote:
> > It's not a good idea to do the check of whether Rx/Tx offload is
> > enabled at the data path. Instead, we could do the check at init
> > stage and store the result, so that we could avoid the check again
> > and again at the critical datapath.
> > 
> > Cc: Olivier Matz <olivier.matz@6wind.com>
> > Signed-off-by: Yuanhan Liu <yuanhan.liu@linux.intel.com>
> > ---
> > v2: - rebase on top of the bug fix patches
> >     - define rx/tx_offload as uint8_t instead of int
> > 
> >  drivers/net/virtio/virtio_ethdev.c | 19 +++++++++++++++++++
> >  drivers/net/virtio/virtio_pci.h    |  2 ++
> >  drivers/net/virtio/virtio_rxtx.c   | 31 +++++--------------------------
> >  3 files changed, 26 insertions(+), 26 deletions(-)
> > 
> > diff --git a/drivers/net/virtio/virtio_ethdev.c b/drivers/net/virtio/virtio_ethdev.c
> > index 1505f67..2adae58 100644
> > --- a/drivers/net/virtio/virtio_ethdev.c
> > +++ b/drivers/net/virtio/virtio_ethdev.c
> > @@ -1188,6 +1188,22 @@ rx_func_get(struct rte_eth_dev *eth_dev)
> >  		eth_dev->rx_pkt_burst = &virtio_recv_pkts;
> >  }
> >  
> > +static inline int
> > +rx_offload_enabled(struct virtio_hw *hw)
> > +{
> > +	return vtpci_with_feature(hw, VIRTIO_NET_F_GUEST_CSUM) ||
> > +		vtpci_with_feature(hw, VIRTIO_NET_F_GUEST_TSO4) ||
> > +		vtpci_with_feature(hw, VIRTIO_NET_F_GUEST_TSO6);
> > +}
> > +
> > +static inline int
> > +tx_offload_enabled(struct virtio_hw *hw)
> > +{
> > +	return vtpci_with_feature(hw, VIRTIO_NET_F_CSUM) ||
> > +		vtpci_with_feature(hw, VIRTIO_NET_F_HOST_TSO4) ||
> > +		vtpci_with_feature(hw, VIRTIO_NET_F_HOST_TSO6);
> > +}
> 
> Do we need these functions to be inlined?

Nope, it was done simply by copy & paste. I could remove them in future
version.

> It looks better to do like this, but out of curiosity, do you see a
> performance improvement?

I didn't bother to have a try: I'd assume it brings no (at least
no obvious) improvements.

	--yliu