[dpdk-dev] net/ixgbe: keep interrupt throttling disabled

  The code being removed would enable time-based interrupt throttling for
the first MSI-X interrupt vector.  This would throttle link status
change interrupts for NICs bound to vfio_pci driver; but for
igb_uio driver, rx queue 0 interrupts would be throttled.  This resulted
in inconsistent latencies in a DPDK interrupt mode packet forwarding
application between the 2 drivers.

We'd like DPDK interrupt mode applications to be awaken by
inbound packet interrupts as soon as they are received regardless
of interrupt interval, interrupt throttling should be kept disabled.

Signed-off-by: David Su <david.w.su@intel.com>
---
 drivers/net/ixgbe/ixgbe_ethdev.c |    2 --
 1 files changed, 0 insertions(+), 2 deletions(-)
  

Hi, David

The code to be removed set the minimum interrupt interval of queue 0 to 0x79E.
According to datasheet, this value has something wrong because it wirte the least 
reserved 3 bits to 110. Anyway, it intends to set a non-zero minimum interrupt interval.

ixgbe_configure_msix( ) is only called by ixgbe_dev_start( ).
After it is called, ixgbe_dev_rx_ini( ) is called.
And ixgbe_set_rsc( ) is called in ixgbe_dev_rx_init( ).
In ixgbe_set_rsc( ), if RSC is enabled, the ITR (interrupt interval) is set to 500us again.

So I think enabling immediate interrupt response by removing these codes is not suitable.
It should be done in other code where interrupt mode Rx is configured.

> Subject: [dpdk-dev] [PATCH] net/ixgbe: keep interrupt throttling disabled
> 
> The code being removed would enable time-based interrupt throttling for the
> first MSI-X interrupt vector.  This would throttle link status change interrupts
> for NICs bound to vfio_pci driver; but for igb_uio driver, rx queue 0 interrupts
> would be throttled.  This resulted in inconsistent latencies in a DPDK interrupt
> mode packet forwarding application between the 2 drivers.
> 
> We'd like DPDK interrupt mode applications to be awaken by inbound packet
> interrupts as soon as they are received regardless of interrupt interval,
> interrupt throttling should be kept disabled.
> 
> Signed-off-by: David Su <david.w.su@intel.com>
> ---
>  drivers/net/ixgbe/ixgbe_ethdev.c |    2 --
>  1 files changed, 0 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ixgbe/ixgbe_ethdev.c
> b/drivers/net/ixgbe/ixgbe_ethdev.c
> index bdf4e2b..fdfb7a6 100644
> --- a/drivers/net/ixgbe/ixgbe_ethdev.c
> +++ b/drivers/net/ixgbe/ixgbe_ethdev.c
> @@ -5815,8 +5815,6 @@ ixgbe_configure_msix(struct rte_eth_dev *dev)
>  	default:
>  		break;
>  	}
> -	IXGBE_WRITE_REG(hw, IXGBE_EITR(IXGBE_MISC_VEC_ID),
> -			IXGBE_MIN_INTER_INTERRUPT_INTERVAL_DEFAULT & 0xFFF);
> 
>  	/* set up to autoclear timer, and the vectors */
>  	mask = IXGBE_EIMS_ENABLE_MASK;
> --
> 1.7.0.4