On Thu, 23 Oct 2008, Eric Dumazet wrote:
SLUB touches objects by default when allocating. And it does it immediately
in slab_alloc() in order to retrieve the pointer to the next object. So
there is no point of hinting there right now.
Please note SLUB touches by reading object.
prefetchw() gives a hint to cpu saying this cache line is going to be
*modified*, even
if first access is a read. Some architectures can save some bus transactions,
acquiring
the cache line in an exclusive way instead of shared one.
Most architectures actually can do that. Its probably worth to run some
tests with that. Conversion of a cacheline from shared to exclusive can
cost something.
If we go to the pointer arrays then the situation is similar to SLAB where
the object is not touched by the allocator. Then the hint would be useful
again.
It is usefull right now for ((SLAB_DESTROY_BY_RCU | SLAB_POISON) or ctor
caches.
Correct.
Probably not that important because many objects are very large anyway, and a
prefetchw()
of the begining of object is partial.
Right.
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