Messages in this thread | | | Date | Wed, 24 Oct 2007 21:35:33 -0700 | From | Arjan van de Ven <> | Subject | Re: Is gcc thread-unsafe? |
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On Wed, 24 Oct 2007 21:29:56 -0700 "David Schwartz" <davids@webmaster.com> wrote:
> > > Well that's exactly right. For threaded programs (and maybe even > > real-world non-threaded ones in general), you don't want to be > > even _reading_ global variables if you don't need to. Cache misses > > and cacheline bouncing could easily cause performance to completely > > tank in some cases while only gaining a cycle or two in > > microbenchmarks for doing these funny x86 predication things. > > For some CPUs, replacing an conditional branch with a conditional > move is a *huge* win because it cannot be mispredicted.
please name one... Hint: It's not one made by either Intel or AMD in the last 4 years...
> In general, > compilers should optimize for unshared data since that's much more > common in typical code. Even for shared data, the usual case is that > you are going to access the data few times, so pulling the cache line > to the CPU is essentially free since it will happen eventually.
it's not about pulling it to the CPU, it's pulling it *out* of all the other cpus AS WELL. (and writing it back to memory, taking away memory bandwidth)
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