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From: John Baldwin <jhb@freebsd.org>
To: freebsd-net@freebsd.org
Subject: Re: ixgbe & msi/x
Date: Mon, 28 Jan 2013 11:14:09 -0500
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 (bigwig.baldwin.cx); Mon, 28 Jan 2013 13:58:24 -0500 (EST)
Cc: net@freebsd.org, Vijay Singh <vijju.singh@gmail.com>
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On Monday, January 28, 2013 1:39:53 am Vijay Singh wrote:
> I am investigating an issue where the ixgbe (82599) device is hung and
> I think I have traced it to the driver not getting interrupts. I have
> MSI/X enabled, with 2 rx/tx queues.
> 
> I am trying to understand this bit of code in the MSI/X setup:
> 
>         if (ixgbe_enable_msix)  {
>                 ixgbe_configure_ivars(adapter);
>                 /* Set up auto-mask */                <<== THIS BIT
>                 if (hw->mac.type == ixgbe_mac_82598EB)
>                         IXGBE_WRITE_REG(hw, IXGBE_EIAM, 
IXGBE_EICS_RTX_QUEUE);
>                 else {
>                         IXGBE_WRITE_REG(hw, IXGBE_EIAM_EX(0), 0xFFFFFFFF);
>                         IXGBE_WRITE_REG(hw, IXGBE_EIAM_EX(1), 0xFFFFFFFF);
>                 }
>         }
> 
> Does this mean that ixgbe_disable_queue() is not needed in the msi/x
> interrupt handler - ixgbe_msix_que()?

You are really going to need the datasheet for this adapter to tell.  From my 
recent reading of the datasheet for igb(4) (which is likely similar), it 
appears that MSI interrupts on that device are configured to auto-clear bits 
in the interrupt cause registers (ICR and EICR) when an MSI interrupt is 
posted so that the interrupt handler doesn't have to do a read of these 
registers to clear their status bits (one of the points of MSI interrupts is 
that you can just access in-memory descriptor rings when the handler fires 
without needing to do a read of the PCI device to force any posted memory 
writes by the device to flush).  If I had to wager a guess, I'd say that ixgbe 
was following the same model.

-- 
John Baldwin