Re: [dpdk-dev] [PATCH RFC] mbuf: Adjust TX flags to start at bit 32

[Neil Horman <nhorman@tuxdriver.com>]

On Wed, Oct 01, 2014 at 09:47:21AM +0100, Bruce Richardson wrote:
> On Tue, Sep 30, 2014 at 01:06:32PM -0400, Neil Horman wrote:
> > On Tue, Sep 30, 2014 at 04:26:02PM +0100, Bruce Richardson wrote:
> > > This patch takes the existing TX flags defined for the mbuf and shifts
> > > each uniquely defined one left so that additional RX flags can be
> > > defined without having RX and TX flags mixed together.
> > > 
> > > Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> > > ---
> > >  lib/librte_mbuf/rte_mbuf.h | 26 +++++++++++++-------------
> > >  1 file changed, 13 insertions(+), 13 deletions(-)
> > > 
> > > diff --git a/lib/librte_mbuf/rte_mbuf.h b/lib/librte_mbuf/rte_mbuf.h
> > > index 1c6e115..c9fc4ec 100644
> > > --- a/lib/librte_mbuf/rte_mbuf.h
> > > +++ b/lib/librte_mbuf/rte_mbuf.h
> > > @@ -86,26 +86,26 @@ extern "C" {
> > >  #define PKT_RX_IEEE1588_PTP  0x0200 /**< RX IEEE1588 L2 Ethernet PT Packet. */
> > >  #define PKT_RX_IEEE1588_TMST 0x0400 /**< RX IEEE1588 L2/L4 timestamped packet.*/
> > >  
> > > -#define PKT_TX_VLAN_PKT      0x0800 /**< TX packet is a 802.1q VLAN packet. */
> > > -#define PKT_TX_IP_CKSUM      0x1000 /**< IP cksum of TX pkt. computed by NIC. */
> > > -#define PKT_TX_IPV4_CSUM     0x1000 /**< Alias of PKT_TX_IP_CKSUM. */
> > > -#define PKT_TX_IPV4          PKT_RX_IPV4_HDR /**< IPv4 with no IP checksum offload. */
> > > -#define PKT_TX_IPV6          PKT_RX_IPV6_HDR /**< IPv6 packet */
> > > +#define PKT_TX_VLAN_PKT  (0x0001 << 32) /**< TX packet is a 802.1q VLAN packet. */
> > > +#define PKT_TX_IP_CKSUM  (0x0002 << 32) /**< IP cksum of TX pkt. computed by NIC. */
> > > +#define PKT_TX_IPV4_CSUM PKT_TX_IP_CKSUM /**< Alias of PKT_TX_IP_CKSUM. */
> > > +#define PKT_TX_IPV4      PKT_RX_IPV4_HDR /**< IPv4 with no IP checksum offload. */
> > > +#define PKT_TX_IPV6      PKT_RX_IPV6_HDR /**< IPv6 packet */
> > >  
> > >  /*
> > > - * Bit 14~13 used for L4 packet type with checksum enabled.
> > > + * Bit 35~34 used for L4 packet type with checksum enabled.
> > >   *     00: Reserved
> > >   *     01: TCP checksum
> > >   *     10: SCTP checksum
> > >   *     11: UDP checksum
> > >   */
> > > -#define PKT_TX_L4_MASK       0x6000 /**< Mask bits for L4 checksum offload request. */
> > > -#define PKT_TX_L4_NO_CKSUM   0x0000 /**< Disable L4 cksum of TX pkt. */
> > > -#define PKT_TX_TCP_CKSUM     0x2000 /**< TCP cksum of TX pkt. computed by NIC. */
> > > -#define PKT_TX_SCTP_CKSUM    0x4000 /**< SCTP cksum of TX pkt. computed by NIC. */
> > > -#define PKT_TX_UDP_CKSUM     0x6000 /**< UDP cksum of TX pkt. computed by NIC. */
> > > -/* Bit 15 */
> > > -#define PKT_TX_IEEE1588_TMST 0x8000 /**< TX IEEE1588 packet to timestamp. */
> > > +#define PKT_TX_L4_NO_CKSUM   (0x0000 << 32) /**< Disable L4 cksum of TX pkt. */
> > > +#define PKT_TX_TCP_CKSUM     (0x0004 << 32) /**< TCP cksum of TX pkt. computed by NIC. */
> > > +#define PKT_TX_SCTP_CKSUM    (0x0008 << 32) /**< SCTP cksum of TX pkt. computed by NIC. */
> > > +#define PKT_TX_UDP_CKSUM     (0x000C << 32) /**< UDP cksum of TX pkt. computed by NIC. */
> > > +#define PKT_TX_L4_MASK       (0x000C << 32) /**< Mask for L4 cksum offload request. */
> > > +/* Bit 36 */
> > > +#define PKT_TX_IEEE1588_TMST (0x0010 << 32) /**< TX IEEE1588 packet to timestamp. */
> > >  
> > >  /* Use final bit of flags to indicate a control mbuf */
> > >  #define CTRL_MBUF_FLAG       (1ULL << 63)
> > > -- 
> > > 1.9.3
> > > 
> > > 
> > 
> > I'm not opposed to the patch at all, but I would like to point out that this is
> > the sort of change that breaks ABI very easily (which is fine right now given
> > the mbuf changes already staged for the release, but still something to be aware
> > of).  As such, are there advantages to this patch (other than the niceness of
> > human readability)?
> > 
> > If we're going to reshuffle these flags now, it might be nice to start tx flags
> > at the most significant bit and count back, and start rx flags at the least
> > significant bit and count up.  That would ensure that we don't reserve flags for
> > a direction without need.
> > 
> > Best
> > Neil
> >
> Good idea, though currently the most significant bit is being used as a flag 
> to indicate a control mbuf. My thinking is that we may potentially need 
> other flags that are not just for RX or TX, and to have those at the end.  
> However, given that that is likely to be the exception case, perhaps we 
> could reserve the last byte for non-RX/TX flags and then implement the 
> scheme you suggest. What do you think?
> 
Sure, seems reasonable
Neil

> /Bruce 
>