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SubjectRe: [RFC][PATCH 6/8] mm: handle_speculative_fault()


On Fri, 8 Jan 2010, Christoph Lameter wrote:
>
> And I made the point that starvation was a hardware issue due to immature
> cacheline handling. Now the software patchup job for the hardware breakage
> is causing regressions for everyone.

Well, in all fairness, (a) existing hardware doesn't do a good job, and
would have a really hard time doing so in general (ie the whole issue of
on-die vs directly-between-sockets vs between-complex-fabric), and (b) in
this case, the problem really was that the x86-64 rwsems were badly
implemented.

The fact that somebody _thought_ that it might be ok to do them with
spinlocks and had done some limited testing without ever hitting the
problem spot (probably never having tested any amount of contention at
all) is immaterial. We should have had real native rwsemaphores for
x86-64, and complaining about the fallback sucking under load is kind of
pointless.

Linus


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