Messages in this thread | | | From | Linus Torvalds <> | Date | Fri, 23 Mar 2012 21:25:04 -0700 | Subject | Re: [GIT PULL] RCU changes for v3.4 |
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On Fri, Mar 23, 2012 at 9:17 PM, Paul E. McKenney <paulmck@linux.vnet.ibm.com> wrote: > > I must admit that __this_cpu_inc() would be nicer than __this_cpu_add(), > though, will fix. I need the leading "__" to avoid disabling preemption > needlessly on non-x86 platforms.
Yeah, that's just bogus. Ok on that.
> The reason that the "__raw" forms are > safe in this case is because the per-CPU variable is saved and restored > at context-switch time. > > Or am I still missing something here?
It's not that the "__raw" forms are "safe". It's that they are SH*T.
Don't use them. They are crap. Why would you do
+ __raw_get_cpu_var(rcu_read_lock_nesting) = + current->rcu_read_lock_nesting_save;
which is just crazy and cannot use the actual sane "%fs:" segment overrides, but instead has to do idiotic "ready the per-cpu offset pointer and add it in".
We've got "__this_cpu_write()" which generates the correct code.
Rule of thumb: there is _never_ any good reason to use __raw_get_cpu_var. It's a broken interface.
Linus -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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