Hi, On Mon, Apr 12, 2010 at 06:32:47PM +0100, Russell King - ARM Linux wrote: > 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.
If I've followed these threads [1][2] correctly, this ARM11 MPCore issue was discovered while running the "KGDB: internal test suite" (KGDB_TESTS) and that problem is resolved via "kgdb: use atomic_inc and atomic_dec instead of atomic_set" [3]. If so, isn't the original ARM11 MPCore KGDB cpu_relax() issue just a red herring? Shouldn't any polling loops which depend on specific (hardware) write/read order implement appropriate barriers rather than rely on cpu_relax() to guarantee order? If perhaps there are indeed other cases where cpu_relax() is being used incorrectly, then maybe those should be fixed instead? Just curious... > 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? Thanks! -- Regards, George [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2010-March/010691.html [2] http://lists.infradead.org/pipermail/linux-arm-kernel/2010-March/011076.html [3] http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commitdiff_plain;h=ae6bf53e0255c8ab04b6fe31806e318432570e3c ------------------------------------------------------------------------------ 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
