linux-kernel - Re: [PATCH 4/4] fm10k/igb/ixgbe: Use fast

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Message-ID: <1416259940.2431.4.camel@jtkirshe-mobl.jf.intel.com>
Date:	Mon, 17 Nov 2014 13:32:20 -0800
From:	Jeff Kirsher <jeffrey.t.kirsher@...el.com>
To:	Alexander Duyck <alexander.h.duyck@...hat.com>
Cc:	linux-arch@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org, mathieu.desnoyers@...ymtl.ca,
	peterz@...radead.org, benh@...nel.crashing.org,
	heiko.carstens@...ibm.com, mingo@...nel.org, mikey@...ling.org,
	linux@....linux.org.uk, donald.c.skidmore@...el.com,
	matthew.vick@...el.com, geert@...ux-m68k.org, romieu@...zoreil.com,
	paulmck@...ux.vnet.ibm.com, nic_swsd@...ltek.com,
	will.deacon@....com, michael@...erman.id.au, tony.luck@...el.com,
	torvalds@...ux-foundation.org, oleg@...hat.com,
	schwidefsky@...ibm.com, fweisbec@...il.com, davem@...emloft.net
Subject: Re: [PATCH 4/4] fm10k/igb/ixgbe: Use fast_rmb on Rx descriptor reads

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@...el.com>
> Cc: Matthew Vick <matthew.vick@...el.com>
> Cc: Don Skidmore <donald.c.skidmore@...el.com>
> Signed-off-by: Alexander Duyck <alexander.h.duyck@...hat.com>
> ---
>  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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