Re: [PATCH -v5][RFC]: mutex: implement adaptive spinning

[Dave Kleikamp]

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:

#ifdef CONFIG_DEBUG_PAGEALLOC
                /*
                 * 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))
                        break;
#else
		cpu = thread->cpu;
#endif

Shaggy
-- 
David Kleikamp
IBM Linux Technology Center

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