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From: "Richardson, Bruce" <bruce.richardson@intel.com>
To: Neil Horman <nhorman@tuxdriver.com>
Thread-Topic: [dpdk-dev] [PATCH 3/5] testpmd: Change rxfreet default to 32
Thread-Index: AQHP0l5oUFb5FU7UokiprGez8jDZ8pwFYuqAgAASbWA=
Date: Thu, 18 Sep 2014 15:53:33 +0000
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Cc: "dev@dpdk.org" <dev@dpdk.org>
Subject: Re: [dpdk-dev] [PATCH 3/5] testpmd: Change rxfreet default to 32
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> -----Original Message-----
> From: Neil Horman [mailto:nhorman@tuxdriver.com]
> Sent: Wednesday, September 17, 2014 4:30 PM
> To: Richardson, Bruce
> Cc: dev@dpdk.org
> Subject: Re: [dpdk-dev] [PATCH 3/5] testpmd: Change rxfreet default to 32
>=20
> On Wed, Sep 17, 2014 at 11:01:40AM +0100, Bruce Richardson wrote:
> > To improve performance by using bulk alloc or vectored RX routines, we
> > need to set rx free threshold (rxfreet) value to 32, so make this the
> > testpmd default.
> >
> > Signed-off-by: Bruce Richardson <bruce.richardson@intel.com>
> > ---
> > app/test-pmd/testpmd.c | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/app/test-pmd/testpmd.c b/app/test-pmd/testpmd.c
> > index 9f6cdc4..5751607 100644
> > --- a/app/test-pmd/testpmd.c
> > +++ b/app/test-pmd/testpmd.c
> > @@ -225,7 +225,7 @@ struct rte_eth_thresh tx_thresh =3D {
> > /*
> > * Configurable value of RX free threshold.
> > */
> > -uint16_t rx_free_thresh =3D 0; /* Immediately free RX descriptors by d=
efault. */
> > +uint16_t rx_free_thresh =3D 32; /* Refill RX descriptors once every 32=
packets
> */
> >
>=20
> Why 32? Was that an experimentally determined value? Does it hold true =
for all
> PMD's?
This is primarily for the ixgbe PMD, which is right now the most highly tun=
ed driver, but it works fine for all other ones too, as far as I'm aware. B=
asically, this is the minimum setting needed to enable either the bulk allo=
c or vector RX routines inside the ixgbe driver, so it's best made the defa=
ult for that reason. Please see " check_rx_burst_bulk_alloc_preconditions()=
" in ixgbe_rxtx.c, and RX function assignment logic in "ixgbe_dev_rx_queue_=
setup()" in the same file.=20
/Bruce