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fm10k/igb/ixgbe: Use dma_rmb on Rx descriptor reads

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This change makes it so that dma_rmb is used when reading the Rx
descriptor.  The advantage of dma_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 coherent 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: Matthew Vick <matthew.vick@intel.com>
Cc: Don Skidmore <donald.c.skidmore@intel.com>
Acked-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: Alexander Duyck <alexander.h.duyck@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Alexander Duyck 2014-12-11 15:02:28 -08:00 committed by David S. Miller
parent a075013870
commit 124b74c18e
3 changed files with 10 additions and 11 deletions
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6
drivers/net/ethernet/intel/fm10k/fm10k_main.c
View file

@ -615,14 +615,14 @@ static bool fm10k_clean_rx_irq(struct fm10k_q_vector *q_vector,
rx_desc = FM10K_RX_DESC(rx_ring, rx_ring->next_to_clean);
if (!fm10k_test_staterr(rx_desc, FM10K_RXD_STATUS_DD))
if (!rx_desc->d.staterr)
break;
/* This memory barrier is needed to keep us from reading
* any other fields out of the rx_desc until we know the
* RXD_STATUS_DD bit is set
* descriptor has been written back
*/
rmb();
dma_rmb();
/* retrieve a buffer from the ring */
skb = fm10k_fetch_rx_buffer(rx_ring, rx_desc, skb);

6
drivers/net/ethernet/intel/igb/igb_main.c
View file

@ -6910,14 +6910,14 @@ static bool igb_clean_rx_irq(struct igb_q_vector *q_vector, const int budget)
rx_desc = IGB_RX_DESC(rx_ring, rx_ring->next_to_clean);
if (!igb_test_staterr(rx_desc, E1000_RXD_STAT_DD))
if (!rx_desc->wb.upper.status_error)
break;
/* This memory barrier is needed to keep us from reading
* any other fields out of the rx_desc until we know the
* RXD_STAT_DD bit is set
* descriptor has been written back
*/
rmb();
dma_rmb();
/* retrieve a buffer from the ring */
skb = igb_fetch_rx_buffer(rx_ring, rx_desc, skb);

9
drivers/net/ethernet/intel/ixgbe/ixgbe_main.c
View file

@ -2009,15 +2009,14 @@ static int ixgbe_clean_rx_irq(struct ixgbe_q_vector *q_vector,
rx_desc = IXGBE_RX_DESC(rx_ring, rx_ring->next_to_clean);
if (!ixgbe_test_staterr(rx_desc, IXGBE_RXD_STAT_DD))
if (!rx_desc->wb.upper.status_error)
break;
/*
* This memory barrier is needed to keep us from reading
/* This memory barrier is needed to keep us from reading
* any other fields out of the rx_desc until we know the
* RXD_STAT_DD bit is set
* descriptor has been written back
*/
rmb();
dma_rmb();
/* retrieve a buffer from the ring */
skb = ixgbe_fetch_rx_buffer(rx_ring, rx_desc);