Message-ID: <1416259940.2431.4.camel@jtkirshe-mobl.jf.intel.com>
Subject: Re: [PATCH 4/4] fm10k/igb/ixgbe: Use fast_rmb on Rx descriptor reads
From: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
To: Alexander Duyck <alexander.h.duyck@redhat.com>
Cc: linux-arch@vger.kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, mathieu.desnoyers@polymtl.ca,
        peterz@infradead.org, benh@kernel.crashing.org,
        heiko.carstens@de.ibm.com, mingo@kernel.org, mikey@neuling.org,
        linux@arm.linux.org.uk, donald.c.skidmore@intel.com,
        matthew.vick@intel.com, geert@linux-m68k.org, romieu@fr.zoreil.com,
        paulmck@linux.vnet.ibm.com, nic_swsd@realtek.com, will.deacon@arm.com,
        michael@ellerman.id.au, tony.luck@intel.com,
        torvalds@linux-foundation.org, oleg@redhat.com, schwidefsky@de.ibm.com,
        fweisbec@gmail.com, davem@davemloft.net
Date: Mon, 17 Nov 2014 13:32:20 -0800
In-Reply-To: <20141117171839.22333.25487.stgit@ahduyck-server>
References: <20141117171005.22333.96544.stgit@ahduyck-server>
	 <20141117171839.22333.25487.stgit@ahduyck-server>
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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.
>=20
> 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.
>=20
> Cc: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
> Cc: Matthew Vick <matthew.vick@intel.com>
> Cc: Don Skidmore <donald.c.skidmore@intel.com>
> Signed-off-by: Alexander Duyck <alexander.h.duyck@redhat.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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