AFAIK, just about everybody writing high performance multiprocess/thread code that relies heavily on mutexes makes some use of user-mode spin-locking.
It's essential if you have N processes contending for a single mutex which they will hold for very short periods of time. Asking the kernel to put you to sleep until the mutex is available means progress is limited by the rate at which the OS can wake up processes. If the mutex is only going to be held for a few dozen cycles (say, to increment the heads of a few queues) then the throughput cost could be considerable over simply spinning a few nanoseconds in user mode until the mutex is available.
And yes, the need becomes more acute if you want to be sure you'll get reasonable performance across a broad range of platforms and their corresponding scheduling policies.
It's essential if you have N processes contending for a single mutex which they will hold for very short periods of time. Asking the kernel to put you to sleep until the mutex is available means progress is limited by the rate at which the OS can wake up processes. If the mutex is only going to be held for a few dozen cycles (say, to increment the heads of a few queues) then the throughput cost could be considerable over simply spinning a few nanoseconds in user mode until the mutex is available.
And yes, the need becomes more acute if you want to be sure you'll get reasonable performance across a broad range of platforms and their corresponding scheduling policies.