On Wed, Jan 25, 2006 at 10:54:08AM +0100, Eric Dumazet wrote:

Nick Piggin a ecrit :

quoted

@@ -2604,10 +2604,10 @@ static inline void *__cache_alloc(kmem_c

	local_irq_save(save_flags);
	objp = ____cache_alloc(cachep, flags);
+	prefetchw(objp);
	local_irq_restore(save_flags);
	objp = cache_alloc_debugcheck_after(cachep, flags, objp,
					    __builtin_return_address(0));
-	prefetchw(objp);
	return objp;
}

I'm not sure why you moved this prefetchw(obj) : This is not related to 
your 'non-refcounting' part, is it ?

Stray hunk. Thanks.

Nick

When I added this prefetchw in slab code, I did place it *after* the 
local_irq_restore(save_flags); because I was not sure if the 
serialization/barrier (popf) would force the cpu (x86/x86_64 in mind) to 
either :
- finish all the loads (even if they are speculative/hints) (so giving a 
bad latency)
- cancel the speculative loads (so prefetchw() *before* the 
local_irq_restore() would be useless.

Makes sense.

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