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Date: Thu, 11 Dec 2003 07:56:11 -0800
From: William Lee Irwin III <wli@holomorphy.com>
To: Nick Piggin <piggin@cyberone.com.au>
Cc: linux-kernel <linux-kernel@vger.kernel.org>,
       Ingo Molnar <mingo@redhat.com>, Rusty Russell <rusty@rustcorp.com.au>,
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       "Martin J. Bligh" <mbligh@aracnet.com>,
       "Nakajima, Jun" <jun.nakajima@intel.com>, Mark Wong <markw@osdl.org>
Subject: Re: [CFT][RFC] HT scheduler
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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