On 02/21/2014 12:28 PM, Peter Zijlstra wrote:
On Mon, Feb 17, 2014 at 03:41:24PM -0500, Waiman Long wrote:+ struct { + u8 lock; /* Lock bit */ + u8 wait; /* Waiting bit */ + u16 qcode; /* Queue code */ + };16 bit code would result in 14 bits for the CPU number, that's only 16k, I think SGI actually had a machine with that many CPUs in.
If NR_CPUS >= 16k, the 2-task optimized code path will be disabled. However, with that many CPUs, it is high spinlock contention behavior that is more important than a bit better performance at low contention level.
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