On Tue, May 09, 2017 at 07:08:01PM +0800, Yubin Ruan wrote: > On Mon, May 08, 2017 at 08:50:52AM -0700, Paul E. McKenney wrote: > > On Mon, May 08, 2017 at 09:25:28PM +0800, Yubin Ruan wrote: > > > On Mon, May 01, 2017 at 08:58:16AM -0700, Paul E. McKenney wrote: > > > > On Sat, Apr 29, 2017 at 10:26:05PM +0800, Yubin Ruan wrote: > > > > [ . . . ] > > > > > Hmm...that reminds me of some words in the perfbook. In the answer of quick quiz 4.17, > > > you state that: > > > > > > Memory barrier only enforce ordering among multiple memory references: They do > > > absolutely nothing to expedite the propogation of data from one part of the system > > > to another. This leads to a quick rule of thumb: You do not need memory barriers > > > unless you are using more than one variable to communicate between multiple threads. > > > > > > Is that only true for the Alpha processor? I mean, on platforms other than > > > Alpha (e.g x86), memory barrier *do* expedite the propogation of data from one > > > processor/core to other processor/core, even though that is not officially documented. > > > > Can you point me at any unofficial documentation of this, for example, > > any performance measurements indicating that (for example) the mfence > > instruction speeds up the propagation of previous writes to other CPUs? > > Hmm...I might had had too much drug at that moment. What I mean is that, on platform > like x86, memory barrier instructions(e.g sfence) enforce that the order of some memory > references are preserved as the same as in the origin processor by another processors. > However, any speedup is not guaranteed. Hey, I was hoping! ;-) Thanx, Paul > Regards, > Yubin > > > In the absence of such documentation, all I can really do is change > > "They do absolutely nothing to expedite..." to something like "They are > > not guaranteed to do anything to expedite..." > > > > Thanx, Paul > > > > > --- > > > Yubin > > > > > > > > > > > > > [1]: https://www.cs.umd.edu/~pugh/java/memoryModel/AlphaReordering.html > > > > > > > > > > > > > > > -- To unsubscribe from this list: send the line "unsubscribe perfbook" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
