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SubjectRe: [openib-general] [PATCH 39 of 39] IB/ipath - use streaming copy in RDMA interrupt handler to reduce packet loss
This is intended to be an architecture specific function
so if the CPU does support HW dma to the CPU's L2 cache, the
architecture specific version of memcpy_nc() would not replace
the default definition which maps memcpy_nc() to memcpy().

For CPUs like the vast majority currently available, there
is a performance benefit by not reading data into the cache
that won't be read a second time.

On Thu, 2006-06-29 at 16:46 -0700, David Miller wrote:
> From: Bryan O'Sullivan <>
> Date: Thu, 29 Jun 2006 16:34:23 -0700
> > I'm not quite following you, though I assume you're referring to Niagara
> > or Rock :-) Are you saying a memcpy_nc would do worse than plain
> > memcpy, or worse than some other memcpy-like routine?
> It would do worse than memcpy.
> If you bypass the L2 cache, it's pointless because the next
> agent (PCI controller, CPU thread, etc.) is going to need the
> data in the L2 cache.
> It's better in that kind of setup to eat the L2 cache miss overhead in
> memcpy since memcpy can usually prefetch and store buffer in order to
> absorb some of the L2 miss costs.
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