Hi Russell, > On Mon, Apr 12, 2010 at 06:23:58PM +0100, Will Deacon wrote: > > This patch changes the definition of cpu_relax() to smp_mb() for ARMv6 > > cores, > > forcing the write buffer to drain while inside a polling loop on an SMP > > system. > > If the Kernel is not compiled for SMP support, this will expand to a > > barrier() > > as before. > > Linus asked how expensive (in terms of power rather than performance) > this was; so far that question has remained unanswered. Can someone > please answer his question?
I gave my opinion on the potential performance impact here: http://sourceforge.net/mailarchive/message.php?msg_name=000001cada64%24b9f84200%242de8c600%24%40deacon%40arm.com To summarise: in the context of polling loops, I believe that the performance impact of adding an smp_mb() to cpu_relax() for v6 SMP is minimal. If cpu_relax() is used in other scenarios, the performance impact can only be reviewed on a case-by-case basis. Are there any other issues that need to be considered, or can I submit this to the patch system? Thanks, Will ------------------------------------------------------------------------------ Download Intel® Parallel Studio Eval Try the new software tools for yourself. Speed compiling, find bugs proactively, and fine-tune applications for parallel performance. See why Intel Parallel Studio got high marks during beta. http://p.sf.net/sfu/intel-sw-dev _______________________________________________ Kgdb-bugreport mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/kgdb-bugreport
