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SubjectRe: [PATCH -v5][RFC]: mutex: implement adaptive spinning
On Wed, 2009-01-07 at 13:58 -0800, Linus Torvalds wrote:
> On Wed, 7 Jan 2009, Peter Zijlstra wrote:
> >
> > Do we really have to re-do all that code every loop?
> No, you're right, we can just look up the cpu once. Which makes Andrew's
> argument that "probe_kernel_address()" isn't in any hot path even more
> true.

Do you need to even do that if CONFIG_DEBUG_PAGEALLOC is unset?
Something like:

* Need to access the cpu field knowing that
* DEBUG_PAGEALLOC could have unmapped it if
* the mutex owner just released it and exited.
if (probe_kernel_address(&thread->cpu, cpu))
cpu = thread->cpu;

David Kleikamp
IBM Linux Technology Center

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