On Wed, 2010-11-17 at 19:53 +0800, Peter Zijlstra wrote: > On Wed, 2010-11-17 at 19:47 +0800, huang ying wrote: > > On Wed, Nov 17, 2010 at 6:40 PM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > > On Wed, 2010-11-17 at 10:18 +0800, Huang Ying wrote: > > >> > > >> cmpxchg has been used in that way by ftrace and perf for a long time. So > > >> I agree to make it a requirement on future architecture ports. > > > > > > Neither mandate an architecture do this though, only that when an > > > architecture wants to support either feature and has NMIs (not all archs > > > have NMI equivalents) it has to be safe. > > > > So we can make sure cmpxchg can be used in lock-less code on > > architectures with perf, irq_work or ftrace enabled? > > It had better, otherwise stuff is broken. Take a look at superh architecture cmpxchg implementation. It seems that cmpxchg is implemented with special instruction if CONFIG_GUSA_RB=y or CONFIG_CPU_SH4A=y, otherwise it is implemented with local_irq_save. Is it possible that superh has not PMU support if CONFIG_GUSA_RB=n and CONFIG_CPU_SH4A=n, so that perf work properly but no NMI safe cmpxchg in that situation? Best Regards, Huang Ying -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
