lkml.org 
[lkml]   [2017]   [Dec]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH 1/1] gianfar: fix a flooded alignment reports because of padding issue.
From
Date
On 12/05/2017 12:06 AM, Claudiu Manoil wrote:
>> -----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;

En, seems more reasonable and clear, feel free to merge it if
convenience, thanks :-)

>
> Do you have any performance numbers for this change?

No performance testing since just padding issue but with
the clear sky of /proc/cpu/alignment in arm side.

Cheers,
Zumeng

>
> Thanks,
> Claudiu


\
 
 \ /
  Last update: 2017-12-05 01:24    [W:0.044 / U:2.524 seconds]
©2003-2018 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site