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

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

> -----Original Message-----
> From: Zoltan Kiss [mailto:zoltan.kiss@linaro.org]
> Sent: Wednesday, July 22, 2015 2:20 PM
> To: Richardson, Bruce
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH v2] ixgbe: fix check for split packets
> 
> 
> 
> On 22/07/15 10:59, Bruce Richardson wrote:
> > 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.
> 
> Ok, then I suggest to make a comment around RTE_IXGBE_VPMD_RX_BURST that
> changing it needs a lot of other changes in the code elsewhere, e.g in
> this split_flags check.
> Btw. vPMD was a bit misleading abbreviation for me, it took me a while
> until I realized 'v' stands for 'vector', not 'virtualization' as in most
> cases nowadays.

Good idea. I'll try to submit a patch to add a comment if I get the chance - otherwise feel free to do so yourself.

As for the naming, yes, I suppose it can be confusing. :-) We possibly need to start calling these pieces of code SSE or AVX rather than just vector, since for some we may end up with multiple vector versions.

/Bruce

> 
> >
> > 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*/
> >>>