Re: [PATCH 4/4] fm10k/igb/ixgbe: Use fast_rmb on Rx descriptor reads

From: Jeff Kirsher
Date: Mon Nov 17 2014 - 16:33:33 EST

On Mon, 2014-11-17 at 09:18 -0800, Alexander Duyck wrote:
> This change makes it so that fast_rmb is used when reading the Rx
> descriptor. The advantage of fast_rmb is that it allows for a much
> lower cost barrier on x86, powerpc, arm, and arm64 architectures than
> a
> traditional memory barrier when dealing with reads that only have to
> synchronize to system memory.
> In addition I have updated the code so that it just checks to see if
> any
> bits have been set instead of just the DD bit since the DD bit will
> always
> be set as a part of a descriptor write-back so we just need to check
> for a
> non-zero value being present at that memory location rather than just
> checking for any specific bit. This allows the code itself to appear
> much
> cleaner and allows the compiler more room to optimize.
> Cc: Jeff Kirsher <jeffrey.t.kirsher@xxxxxxxxx>
> Cc: Matthew Vick <matthew.vick@xxxxxxxxx>
> Cc: Don Skidmore <donald.c.skidmore@xxxxxxxxx>
> Signed-off-by: Alexander Duyck <alexander.h.duyck@xxxxxxxxxx>
> ---
> drivers/net/ethernet/intel/fm10k/fm10k_main.c | 6 +++---
> drivers/net/ethernet/intel/igb/igb_main.c | 6 +++---
> drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 9 ++++-----
> 3 files changed, 10 insertions(+), 11 deletions(-)

Looks like more changes will be coming, based on the feedback on earlier
patches. So I won't be picking this up for validation purposes.

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