diff options
| author | Claudiu Manoil <claudiu.manoil@freescale.com> | 2013-02-14 09:00:04 +0400 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2013-02-14 22:32:24 +0400 |
| commit | bd9e89f29427f4accd62ce5dfe1547549f0d3fbc (patch) | |
| tree | ec80bb806e6ee4412042d8a7badd2891a08cde3e /drivers | |
| parent | b597d20d59b84f0fc3735de75c3efd6e6eb4365d (diff) | |
| download | linux-bd9e89f29427f4accd62ce5dfe1547549f0d3fbc.tar.xz | |
gianfar: GRO_DROP is unlikely
The change is significant since it affects the rx hot path.
Paul observed and documented the effects at asm level, see
below:
"It turns out that it does make a difference, since gfar_process_frame
gets inlined, and so the increment code gets moved out of line (I have
marked the if statment with * and the increment code within "-----"):
------------------------- as is currently ------------------
4d14: 80 61 00 18 lwz r3,24(r1)
4d18: 7f c4 f3 78 mr r4,r30
4d1c: 48 00 00 01 bl 4d1c <gfar_clean_rx_ring+0x10c>
* 4d20: 2f 83 00 04 cmpwi cr7,r3,4
4d24: 40 9e 00 1c bne- cr7,4d40
<gfar_clean_rx_ring+0x130>
----------------------------
4d28: 81 3c 01 f8 lwz r9,504(r28)
4d2c: 81 5c 01 fc lwz r10,508(r28)
4d30: 31 4a 00 01 addic r10,r10,1
4d34: 7d 29 01 94 addze r9,r9
4d38: 91 3c 01 f8 stw r9,504(r28)
4d3c: 91 5c 01 fc stw r10,508(r28)
----------------------------
4d40: a0 1f 00 24 lhz r0,36(r31)
4d44: 81 3f 00 00 lwz r9,0(r31)
4d48: 7f a4 eb 78 mr r4,r29
4d4c: 7f e3 fb 78 mr r3,r31
-------------------------- unlikely ------------------------
4d14: 80 61 00 18 lwz r3,24(r1)
4d18: 7f c4 f3 78 mr r4,r30
4d1c: 48 00 00 01 bl 4d1c <gfar_clean_rx_ring+0x10c>
* 4d20: 2f 83 00 04 cmpwi cr7,r3,4
4d24: 41 9e 03 94 beq- cr7,50b8
<gfar_clean_rx_ring+0x4a8>
4d28: a0 1f 00 24 lhz r0,36(r31)
4d2c: 81 3f 00 00 lwz r9,0(r31)
4d30: 7f a4 eb 78 mr r4,r29
4d34: 7f e3 fb 78 mr r3,r31
[...]
50b8: 81 3c 01 f8 lwz r9,504(r28)
50bc: 81 5c 01 fc lwz r10,508(r28)
50c0: 31 4a 00 01 addic r10,r10,1
50c4: 7d 29 01 94 addze r9,r9
50c8: 91 3c 01 f8 stw r9,504(r28)
50cc: 91 5c 01 fc stw r10,508(r28)
50d0: 4b ff fc 58 b 4d28 <gfar_clean_rx_ring+0x118>
So, the increment does actually get moved ~1k away."
Cc: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Claudiu Manoil <claudiu.manoil@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'drivers')
| -rw-r--r-- | drivers/net/ethernet/freescale/gianfar.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/drivers/net/ethernet/freescale/gianfar.c b/drivers/net/ethernet/freescale/gianfar.c index 592d297b9eda..af0f4d6b9edf 100644 --- a/drivers/net/ethernet/freescale/gianfar.c +++ b/drivers/net/ethernet/freescale/gianfar.c @@ -2740,7 +2740,7 @@ static int gfar_process_frame(struct net_device *dev, struct sk_buff *skb, /* Send the packet up the stack */ ret = napi_gro_receive(napi, skb); - if (GRO_DROP == ret) + if (unlikely(GRO_DROP == ret)) atomic64_inc(&priv->extra_stats.kernel_dropped); return 0; |