Messages in this thread | | | Date | Mon, 20 Aug 2007 16:41:26 -0400 | From | Mathieu Desnoyers <> | Subject | Re: [patch 01/23] Fall back on interrupt disable in cmpxchg8b on 80386 and 80486 |
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* Christoph Lameter (clameter@sgi.com) 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 majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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