Subject: Re: CONFIG_XPS depends on L1_CACHE_BYTES being greater than sizeof(struct xps_map)

From: Helge Deller <[email-masked]>
Date: Fri, 23 Oct 2015 21:25:04 +0200

On 22.10.2015 23:50, Eric Dumazet wrote:
> On Thu, 2015-10-22 at 22:00 +0200, Helge Deller wrote:
>> Hi Tom & David,
>>
>> I've queued-up a patch for the parisc architecture which reduces L1_CACHE_BYTES from 32 to 16:
>>   https://patchwork.kernel.org/patch/7399291/
>>
>> But this change will break the kernel build like this:
>>
>> In file included from net/core/dev.c:92:0:
>> net/core/dev.c: In function ‘expand_xps_map’:
>> include/linux/netdevice.h:721:27: warning: overflow in implicit constant conversion [-Woverflow]
>>    #define XPS_MIN_MAP_ALLOC ((L1_CACHE_BYTES - sizeof(struct xps_map)) \
>> net/core/dev.c:1972:18: note: in expansion of macro ‘XPS_MIN_MAP_ALLOC’
>>    int alloc_len = XPS_MIN_MAP_ALLOC;
>>
>> Do you see an easy way to fix this ?
> 
> 
> Using L2_CACHE_BYTES would be better, but it unfortunately does not
> exist.

Then, how about simply changing it to twice of L1_CACHE_BYTES ?

#define XPS_MIN_MAP_ALLOC ((L1_CACHE_BYTES * 2 - sizeof(struct xps_map)) / sizeof(u16))

Helge