Re: [PATCH net-next 0/3] net: Switch tag HW extraction/insertion

[Florian Fainelli <florian@alphacore.org>]

On 30/07/15 15:51, David Miller wrote:
> From: David Miller <davem@davemloft.net>
> Date: Thu, 30 Jul 2015 14:19:35 -0700 (PDT)
> 
>> This looks fine, series applied, thanks.
> 
> I think your control block is too large, you'll need to rework this
> somehow.

So napi_gro_cb really is 48 bytes on 64-bits architectures (had not
realized it was so big).

What would you recommend to do here considering that this driver is
currently used on 32-bits platforms, but I see no reason why someone
would no want to use this feature on a 64-bit platform, yet we are
competing with napi_gro_cb, and adding a new skbuff member is pretty
much a no-no? Would it be acceptable to have a new member which is ifdef
CONFIG_NET_DSA_TAG_BRCM?

FWIW, this does provide a small 2-3% throughput increase for RX.

> 
> In function ‘dsa_copy_brcm_tag’,
>     inlined from ‘bcm_sysport_desc_rx’ at drivers/net/ethernet/broadcom/bcmsysport.c:707:4,
>     inlined from ‘bcm_sysport_poll’ at drivers/net/ethernet/broadcom/bcmsysport.c:864:12:
> include/linux/compiler.h:447:38: error: call to ‘__compiletime_assert_2016’ declared with attribute error: BUILD_BUG_ON failed: sizeof(skb->cb) - sizeof(struct napi_gro_cb) < BRCM_TAG_LEN
>   _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
>                                       ^
> include/linux/compiler.h:430:4: note: in definition of macro ‘__compiletime_assert’
>     prefix ## suffix();    \
>     ^
> include/linux/compiler.h:447:2: note: in expansion of macro ‘_compiletime_assert’
>   _compiletime_assert(condition, msg, __compiletime_assert_, __LINE__)
>   ^
> include/linux/bug.h:50:37: note: in expansion of macro ‘compiletime_assert’
>  #define BUILD_BUG_ON_MSG(cond, msg) compiletime_assert(!(cond), msg)
>                                      ^
> include/linux/bug.h:74:2: note: in expansion of macro ‘BUILD_BUG_ON_MSG’
>   BUILD_BUG_ON_MSG(condition, "BUILD_BUG_ON failed: " #condition)
>   ^
> include/linux/netdevice.h:2016:2: note: in expansion of macro ‘BUILD_BUG_ON’
>   BUILD_BUG_ON(sizeof(skb->cb) - sizeof(struct napi_gro_cb) < BRCM_TAG_LEN);
>   ^
> scripts/Makefile.build:264: recipe for target 'drivers/net/ethernet/broadcom/bcmsysport.o' failed
> 


-- 
Florian