Yes, the main advantage of Qspinlock code can be observed in NUMA but when I tested in an embedded system, a slight advantage was observed.
------- Original Message ------- Sender : Peter Zijlstra<pet...@infradead.org> Date : May 19, 2015 21:43 (GMT+09:00) Title : Re: [RFC] arm: Add for atomic half word exchange On Tue, May 19, 2015 at 11:20:13AM +0000, Sarbojit Ganguly wrote: > On Tuesday 19 May 2015 09:39:33 Sarbojit Ganguly wrote: > > Since 16 bit half word exchange was not there and MCS based > > qspinlock by Waiman's xchg_tail() requires an atomic exchange on a > > half word, here is a small modification to __xchg() code. Can you actually see a performance improvement with the qspinlock code on ARM ? The real improvements on x86 were on NUMA systems; although there were real improvements on light loads as well. Note that ARM (or any load-store arch) could get rid of all the cmpxchg loops in that code. Although I suppose we replaced the most common ones with these unconditional atomics already -- like that xchg16 -- so implementing those with ll/sc, as you did, should be near optimal. ????? ??? ?? ?? ?? ----------------------------------------------------------------------+ The Tao lies beyond Yin and Yang. It is silent and still as a pool of water. | It does not seek fame, therefore nobody knows its presence. | It does not seek fortune, for it is complete within itself. | It exists beyond space and time. | ----------------------------------------------------------------------+
