* Christoph Lameter ([EMAIL PROTECTED]) wrote: > On Mon, 20 Aug 2007, Mathieu Desnoyers wrote: > > > already present in cmpxchg_386_u32 tells much about how this cmpxchg > > implementation should not be used in a SMP context. However, the > > cmpxchg_local > > can perfectly use this fallback, since it only needs to be atomic wrt the > > local > > cpu. > > Do you have an example where the use of cmpxchg_local is a performance > benefit when actually used in code? cmpxchg is already problematic > functionality since it is not available on all platforms.
Yes, I use it as synchronization mechanism for my buffer management algorithm in LTTng. Since I write in per-cpu buffers and want to be as reentrant as possible wrt other contexts (dealing with NMI as worse case, but also applies to MCE..), I use local_cmpxchg to reserve space in my buffers. It is faster than the standard cmpxchg. Mathieu -- Mathieu Desnoyers Computer Engineering Ph.D. Student, Ecole Polytechnique de Montreal OpenPGP key fingerprint: 8CD5 52C3 8E3C 4140 715F BA06 3F25 A8FE 3BAE 9A68 - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
