Hi Andrew, On Wed, Jan 8, 2014 at 9:36 AM, Andrew Morton <a...@linux-foundation.org> wrote: >> I am wondering if the above patch is more efficient, because: >> >> - raw_local_irq_save()/raw_local_irq_restore() should be cheaper >> than preempt_enable() in theory > > Don't think so - local_irq_disable() requires quite some internal > synchronization in the CPU and is expensive. preempt_disable() is just
Yes, it might be a little expensive on some CPUs, but should be arch-dependent(CPU inside things are involved) > an add+barrier, minus the add if the kernel is non-preemptable. IMO, generally, from software view, local_irq_save() only save the CPU's interrupt mask to the local variable 'flag', and sets irq mask to register, considered local variable can be thought to be in cache, so I think it might be cheaper than preempt_enable() because preempt counter may not be in cache. Also this_cpu_add() won't work in batch path(slow path), we still need to avoid interrupt coming between reading the percpu counter and resetting it, otherwise counts might be lost too, :-) Thanks, -- Ming Lei -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
