On Saturday 17 November 2007 01:03:35 Mathieu Desnoyers wrote: > x86 optimization of the immediate values which uses a movl with code > patching to set/unset the value used to populate the register used as > variable source.
Since immediate values are by definition an optimization, I think it makes sense to insist they be 1, 2, 4 or 8 bytes. A BUILD_BUG_ON() in the right place should ensure this (probably in generic code rather than x86). > =================================================================== > --- linux-2.6-lttng.orig/arch/x86/kernel/traps_32.c I don't think you need any modification to this file now. > + * Create the instruction in a discarded section to calculate its size. This > is > + * how we can align the beginning of the instruction on an address that will > + * permit atomic modificatino of the immediate value without knowing the > size of > + * the opcode used by the compiler. The operand size is known in advance. > + */ This alignment is also now unnecessary. > +++ linux-2.6-lttng/arch/x86/kernel/immediate.c 2007-11-16 > 08:56:22.000000000 -0500 @@ -0,0 +1,143 @@ > +/* > + * Immediate Value - x86 architecture specific code. This is now almost entirely generic code, but I suppose we can let the next architecture hoist it out. > +/** > + * arch_immediate_update_early - update one immediate value at boot time > + * @immediate: pointer of type const struct __immediate to update > + * > + * Update one immediate value at boot time. > + */ > +void arch_immediate_update_early(const struct __immediate *immediate) I think it would be easier to just fast-path the num_online_cpus == 1 case, even if you want to keep this "update_early" interface. But I like your IPI algorithm: very tight. Thanks, Rusty. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
