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| From | "Chris M. Thomasson" <no@spam.invalid> |
| Newsgroups | comp.programming.threads |
| Subject | Re: About my new algorithm |
| Date | Sat, 6 Dec 2014 13:45:56 -0800 |
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| Lines | 42 |
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| References | <m5qvr9$o4v$3@dont-email.me> <m5t191$28r$1@speranza.aioe.org> <slrnm84di2.je0.dave@fly.srk.fer.hr> |
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> "Drazen Kacar" wrote in message > news:slrnm84di2.je0.dave@fly.srk.fer.hr... > > Chris M. Thomasson wrote: > > Comparing RCU read-side with anything that uses an atomic rmw and/or > > memory barrier is just plain foolish. That LOCK ADD destroys > > performance > > when compared to RCU's basically zero overhead reads. End of story. > I don't quite understand the "or" part of your "and/or memory barrier" > statement. If there was a different algorithm which used only memory > barrier, but not RMW, would that be so much worse than RCU? Yes. Anytime you can reduce the number of memory barriers and/or atomics, the better. I have tested RCU verses the same RCU with a single MFENCE instruction on the reader side. The one without the membar slaughtered it wrt reads-per-second per-thread. > Another thing I don't quite understand is in Wikipedia's RCU article (at > http://en.wikipedia.org/wiki/Read-copy-update, section Simple > implementation) > The article says: > [RCU's] read-side overhead is precisely zero, as > smp_read_barrier_depends() > is an empty macro on all but DEC Alpha CPUs;[19] such memory barriers > are > not needed on modern CPUs. > I was under the impression that you'd need memory barrier on Alpha because > it does more agressive memory access reordering than other processors. > But then, if that's correct, that means that modern CPUs (whichever they > are) still don't have features that old Alpha CPUs have. And not the other > way round. Yup. On a DEC Alpha, RCU simply needs a membar for it does not honor data-dependent loads. RCU relies on data-dependences being there.
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About my new algorithm Ramine <ramine@1.1> - 2014-12-04 19:57 -0800
Re: About my new algorithm Ramine <ramine@1.1> - 2014-12-04 20:07 -0800
Re: About my new algorithm "Chris M. Thomasson" <no@spam.invalid> - 2014-12-05 11:32 -0800
Re: About my new algorithm Drazen Kacar <dave@fly.srk.fer.hr> - 2014-12-05 22:48 +0000
Re: About my new algorithm "Chris M. Thomasson" <no@spam.invalid> - 2014-12-06 13:45 -0800
Re: About my new algorithm "Chris M. Thomasson" <no@spam.invalid> - 2014-12-06 13:56 -0800
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