> -----Original Message-----
> From: Wood Scott-B07421
> Sent: Wednesday, December 02, 2015 11:41 PM
>
> On Mon, 2015-11-02 at 19:31 +0200, Madalin Bucur wrote:
> > Allow the selection of the transmission queue based on the CPU id.
>
> Explain why.
I'll add more details in the commit log. This is a customer generated
feature. Bypassing the standard XPS can increase performance by making use
of the DPAA HW particularities.
> >
> > Signed-off-by: Madalin Bucur <madalin.bu...@freescale.com>
> > ---
> > drivers/net/ethernet/freescale/dpaa/Kconfig | 10 ++++++++++
> > drivers/net/ethernet/freescale/dpaa/dpaa_eth.c | 3 +++
> > drivers/net/ethernet/freescale/dpaa/dpaa_eth.h | 6 ++++++
> > drivers/net/ethernet/freescale/dpaa/dpaa_eth_common.c | 8 ++++++++
> > drivers/net/ethernet/freescale/dpaa/dpaa_eth_common.h | 4 ++++
> > 5 files changed, 31 insertions(+)
> >
> > diff --git a/drivers/net/ethernet/freescale/dpaa/Kconfig
> > b/drivers/net/ethernet/freescale/dpaa/Kconfig
> > index 022d5aa..2577aac 100644
> > --- a/drivers/net/ethernet/freescale/dpaa/Kconfig
> > +++ b/drivers/net/ethernet/freescale/dpaa/Kconfig
> > @@ -11,6 +11,16 @@ menuconfig FSL_DPAA_ETH
> >
> > if FSL_DPAA_ETH
> >
> > +config FSL_DPAA_ETH_USE_NDO_SELECT_QUEUE
> > + bool "Use driver's Tx queue selection mechanism"
> > + default y
> > + ---help---
> > + The DPAA Ethernet driver defines a ndo_select_queue() callback
> > for optimal selection
> > + of the egress FQ. That will override the XPS support for this
> > netdevice.
> > + If for whatever reason you want to be in control of the egress FQ
> > -to-CPU selection and mapping,
> > + or simply don't want to use the driver's ndo_select_queue()
> > callback, then unselect this
> > + and use the standard XPS support instead.
>
> Is there a use case for needing this to be configurable?
If the standard XPS is desired, the Kconfig option allows the driver user to
select that.
> > diff --git a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> > b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> > index 31d55b4..894f1a7 100644
> > --- a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> > +++ b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> > @@ -390,6 +390,9 @@ static const struct net_device_ops dpa_private_ops =
> {
> > .ndo_get_stats64 = dpa_get_stats64,
> > .ndo_set_mac_address = dpa_set_mac_address,
> > .ndo_validate_addr = eth_validate_addr,
> > +#ifdef CONFIG_FSL_DPAA_ETH_USE_NDO_SELECT_QUEUE
> > + .ndo_select_queue = dpa_select_queue,
> > +#endif
> > .ndo_change_mtu = dpa_change_mtu,
> > .ndo_set_rx_mode = dpa_set_rx_mode,
> > .ndo_init = dpa_ndo_init,
> > diff --git a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.h
> > b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.h
> > index 1ba6617..87577cf 100644
> > --- a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.h
> > +++ b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.h
> > @@ -420,9 +420,15 @@ static inline void _dpa_assign_wq(struct dpa_fq
> *fq)
> > }
> > }
> >
> > +#ifdef CONFIG_FSL_DPAA_ETH_USE_NDO_SELECT_QUEUE
> > +/* Use in lieu of skb_get_queue_mapping() */
> > +#define dpa_get_queue_mapping(skb) \
> > + raw_smp_processor_id()
> > +#else
> > /* Use the queue selected by XPS */
> > #define dpa_get_queue_mapping(skb) \
> > skb_get_queue_mapping(skb)
> > +#endif
>
> Why is this necessary? Shouldn't providing a custom .ndo_select_queue()
> be
> sufficient to ensure that skb_get_queue_mapping() returns the same thing?
dpa_get_queue_mapping() is used in more than one place, the ndo function cannot
be used directly in all places, the current setup is justified.
> And if this goes away, it's just a matter of a function pointer, so if it
> does
> need to be configurable it could be a runtime option.
>
> -Scott
It's used on the hot path, adding an extra indirection layer to make it
selectable
at runtime would defeat the purpose...
Madalin
