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SubjectRe: [CFT][RFC] HT scheduler
William Lee Irwin III wrote:
>> There is a spinloop in __up_read(), which is probably it.

On Fri, Dec 12, 2003 at 02:51:32AM +1100, Nick Piggin wrote:
> Oh I see - in rwsem_wake?

Even before that:

static inline void __up_read(struct rw_semaphore *sem)
{
__s32 tmp = -RWSEM_ACTIVE_READ_BIAS;
__asm__ __volatile__(
"# beginning __up_read\n\t"
LOCK_PREFIX " xadd %%edx,(%%eax)\n\t" /* subtracts 1, returns the old value */
" js 2f\n\t" /* jump if the lock is being waited upon */
"1:\n\t"
LOCK_SECTION_START("")
"2:\n\t"
" decw %%dx\n\t" /* do nothing if still outstanding active readers
*/
" jnz 1b\n\t"
" pushl %%ecx\n\t"
" call rwsem_wake\n\t"
" popl %%ecx\n\t"
" jmp 1b\n"
LOCK_SECTION_END
"# ending __up_read\n"
: "=m"(sem->count), "=d"(tmp)
: "a"(sem), "1"(tmp), "m"(sem->count)
: "memory", "cc");
}


-- wli
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