The conversion to signed happens with types shorter than int
(__ticket_t is either u8 or u16).
By changing Raghavendra's program to use unsigned short int, you can
see the problem:
================
#include <stdio.h>
#define LOCK_INC 2
int main()
{
unsigned short int head = 32700, tail=2;
if ((tail - head) > LOCK_INC)
printf(" tail - head > LOCK_INC \n");
else
printf(" tail - head < LOCK_INC \n");
return 0;
}
================
gcc -g -o t main.c
./t
tail - head < LOCK_INC
However, having just unsigned int returns the opposite result
(unsigned int head = 32700, tail=2;)
gcc -g -o t main.c
./t
tail - head > LOCK_INC
On Tue, May 5, 2015 at 3:58 AM, Peter Zijlstra <pet...@infradead.org> wrote:
> On Tue, May 05, 2015 at 04:08:22PM +0530, Raghavendra K T wrote:
>> ================
>> #include <stdio.h>
>>
>> #define LOCK_INC 2
>
> Note that to be completely identical to the kernel code you should've
> written:
>
> #define LOCK_INC ((unsigned int)2)
>
> as per:
>
> #define TICKET_LOCK_INC ((__ticket_t)__TICKET_LOCK_INC)
>
>
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