On Mon, Jul 13, 2009 at 11:15:19AM -0700, David Daney wrote: > On some CPUs, it is more efficient to disable and enable interrupts in > the kernel rather than use ll/sc for atomic operations. But if we > were to set cpu_has_llsc to false, we would break the userspace futex > interface (in asm/futex.h). > > We separate the two concepts, with a new predicate kernel_uses_llsc, > that lets us disable the kernel's use of ll/sc while still allowing > the futex code to use it. > > Also there were a couple of cases in bitops.h where we were using > ll/sc unconditionally even if cpu_has_llsc were false. There are > several places in assembly code where the configure variable > CONFIG_CPU_HAS_LLSC is used instead of cpu_has_llsc, so we make > cpu_has_llsc true if CONFIG_CPU_HAS_LLSC is set, for consistency. The uses in bitops.h you mentioned were not bugs; they were wrapped in #ifdef CONFIG_CPU_MIPSR2 and MIPS R2 implies having LL/SC. So for sane setups there just is no point in bothering. As discussed on IRC - this patch adds one more use of CONFIG_CPU_HAS_LLSC which really should die. So I turned the remaining CONFIG_CPU_HAS_LLSC users further upside down, removed CONFIG_CPU_HAS_LLSC and applied your patch with the necessary adjustments on top. Thanks! Ralf
