lkml.org 
[lkml]   [2017]   [Dec]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
SubjectRE: [PATCH 1/1] gianfar: fix a flooded alignment reports because of padding issue.
Date
>-----Original Message-----
>From: Zumeng Chen [mailto:zumeng.chen@gmail.com]
>Sent: Monday, December 04, 2017 5:22 AM
>To: netdev@vger.kernel.org; linux-kernel@vger.kernel.org
>Cc: Claudiu Manoil <claudiu.manoil@nxp.com>; davem@davemloft.net
>Subject: [PATCH 1/1] gianfar: fix a flooded alignment reports because of padding
>issue.
>
>According to LS1021A RM, the value of PAL can be set so that the start of the
>IP header in the receive data buffer is aligned to a 32-bit boundary. Normally,
>setting PAL = 2 provides minimal padding to ensure such alignment of the IP
>header.
>
>However every incoming packet's 8-byte time stamp will be inserted into the
>packet data buffer as padding alignment bytes when hardware time stamping is
>enabled.
>
>So we set the padding 8+2 here to avoid the flooded alignment faults:
>
>root@128:~# cat /proc/cpu/alignment
>User: 0
>System: 17539 (inet_gro_receive+0x114/0x2c0)
>Skipped: 0
>Half: 0
>Word: 0
>DWord: 0
>Multi: 17539
>User faults: 2 (fixup)
>
[...]
>
> drivers/net/ethernet/freescale/gianfar.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)
>
>diff --git a/drivers/net/ethernet/freescale/gianfar.c
>b/drivers/net/ethernet/freescale/gianfar.c
>index e616b71..e47945f 100644
>--- a/drivers/net/ethernet/freescale/gianfar.c
>+++ b/drivers/net/ethernet/freescale/gianfar.c
>@@ -1413,9 +1413,11 @@ static int gfar_probe(struct platform_device *ofdev)
>
> gfar_init_addr_hash_table(priv);
>
>- /* Insert receive time stamps into padding alignment bytes */
>+ /* Insert receive time stamps into padding alignment bytes, and
>+ * plus 2 bytes padding to ensure the cpu alignment.
>+ */
> if (priv->device_flags & FSL_GIANFAR_DEV_HAS_TIMER)
>- priv->padding = 8;
>+ priv->padding = 8 + DEFAULT_PADDING;
>
> if (dev->features & NETIF_F_IP_CSUM ||
> priv->device_flags & FSL_GIANFAR_DEV_HAS_TIMER)
>--
>2.5.0

Why handle only the rx timestamp path (HAS_TIMER) when the issue, as presented
by you, should be applicable to the default path as well?

The code change according to the patch description should be more likely:

+ priv->padding = DEFAULT_PADDING;
/* Insert receive time stamps into padding alignment bytes */
if (priv->device_flags & FSL_GIANFAR_DEV_HAS_TIMER)
- priv->padding = 8;
+ priv->padding += 8;


Do you have any performance numbers for this change?

Thanks,
Claudiu

\
 
 \ /
  Last update: 2017-12-04 17:07    [W:0.089 / U:2.432 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site