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From: "Liang, Cunming" <cunming.liang@intel.com>
To: "Liang, Cunming" <cunming.liang@intel.com>, "Ananyev, Konstantin"
 <konstantin.ananyev@intel.com>, Zoltan Kiss <zoltan.kiss@linaro.org>,
 "dev@dpdk.org" <dev@dpdk.org>
Thread-Topic: [dpdk-dev] [PATCH v1] ixgbe: remove vector pmd burst	size
 restriction
Thread-Index: AQHQzb/jeorioZ4AXUGu3RBLDHAXhZ36CMvA
Date: Mon, 3 Aug 2015 09:59:52 +0000
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Subject: Re: [dpdk-dev] [PATCH v1] ixgbe: remove vector pmd
	burst	size	restriction
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Hi,

[...]
> > Another thing, that I just thought about:
> > Right now we invoke ixgbe_rxq_rearm() only at the start of
> > _recv_raw_pkts_vec().
> > Before it was ok, as _recv_raw_pkts_vec() would never try to read more =
then
> 32
> > RXDs.
> > But what would happen if nb_pkts > rxq->nb_desc and rxq->rxrearm_nb =3D=
=3D 0?
> > I suppose,  _recv_raw_pkts_vec() can wrpa around RXD ring and 'receive'
> same
> > packet twice?
> > So we probably better still limit nb_pkts <=3D 32 at _recv_raw_pkts_vec=
().
>=20
> The _recv_raw_pkts_vec() won't wrap around RXD ring. When it reaches the =
last
> one, the DD bit of padding desc. always 0.
> So in the case nb_pkts > rxq->nb_desc, the '_recv_raw_pkts_vec()' can onl=
y get
> no more than 'rxq->nb_desc' packets.
>=20
I think the violation is true when rx_id in some middle position of desc_ri=
ng, and nb_pkts > rxq->nb_desc.
The DD checking may exceed the boundary (access the entry whose DD is set a=
nd waiting for rearm).
So I agree to keep the max burst size as 32.

/Steve