Re: [dpdk-dev] [PATCH v2] ixgbe: fix check for split packets

[Bruce Richardson <bruce.richardson@intel.com>]

On Wed, Jul 22, 2015 at 10:47:34AM +0100, Zoltan Kiss wrote:
> Hi,
> 
> And what happens if someone changes RTE_IXGBE_VPMD_RX_BURST to something
> else than 32? I guess this bug were introduced when someone raised it from
> 16 to 32

Actually, no, this bug is purely due to me getting my maths wrong when I 
wrote this function. The vector PMD has always worked in bursts of 32 at a
time.

> I think you are better off with a for loop which uses this value. Or at
> least make a comment around RTE_IXGBE_VPMD_RX_BURST that if you change that
> value this check should be modified as well.

The vector PMD always works off a fixed 32 burst size. Any change to that will
lead to many changes in the code, so I don't believe a loop is necessary.

Regards,
/Bruce

> 
> Regards,
> 
> Zoltan
> 
> On 22/07/15 10:13, Bruce Richardson wrote:
> >The check for split packets to be reassembled in the vector ixgbe PMD
> >was incorrectly only checking the first 16 elements of the array instead
> >of all 32. This is fixed by changing the uint32_t values to be uint64_t
> >instead.
> >
> >Fixes: cf4b4708a88a ("ixgbe: improve slow-path perf with vector scattered Rx")
> >
> >Reported-by: Zoltan Kiss <zoltan.kiss@linaro.org>
> >Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> >
> >---
> >V2: Rename variable from split_fl32 to split_fl64 to match type change.
> >---
> >  drivers/net/ixgbe/ixgbe_rxtx_vec.c | 6 +++---
> >  1 file changed, 3 insertions(+), 3 deletions(-)
> >
> >diff --git a/drivers/net/ixgbe/ixgbe_rxtx_vec.c b/drivers/net/ixgbe/ixgbe_rxtx_vec.c
> >index d3ac74a..f2052c6 100644
> >--- a/drivers/net/ixgbe/ixgbe_rxtx_vec.c
> >+++ b/drivers/net/ixgbe/ixgbe_rxtx_vec.c
> >@@ -549,10 +549,10 @@ ixgbe_recv_scattered_pkts_vec(void *rx_queue, struct rte_mbuf **rx_pkts,
> >  		return 0;
> >
> >  	/* happy day case, full burst + no packets to be joined */
> >-	const uint32_t *split_fl32 = (uint32_t *)split_flags;
> >+	const uint64_t *split_fl64 = (uint64_t *)split_flags;
> >  	if (rxq->pkt_first_seg == NULL &&
> >-			split_fl32[0] == 0 && split_fl32[1] == 0 &&
> >-			split_fl32[2] == 0 && split_fl32[3] == 0)
> >+			split_fl64[0] == 0 && split_fl64[1] == 0 &&
> >+			split_fl64[2] == 0 && split_fl64[3] == 0)
> >  		return nb_bufs;
> >
> >  	/* reassemble any packets that need reassembly*/
> >