Messages in this thread | | | Date | Tue, 20 Sep 2011 11:08:56 -0500 (CDT) | From | Christoph Lameter <> | Subject | Re: [RFC][PATCH 0/5] Introduce checks for preemptable code for this_cpu_read/write() |
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On Tue, 20 Sep 2011, Steven Rostedt wrote:
> On Tue, 2011-09-20 at 09:57 -0500, Christoph Lameter wrote: > > > this_cpu_xx functions are made for those locations that have > > preemption enabled. If you can use those function (classic case is a > > per cpu counter increment in the network subsystem) then you can avoid > > preempt disable/enable or get_cpu/put_cpu. > > If the variables are used for a very short time, then the latencies > introduced by a simple: > > var = get_cpu_var(my_var); > if (var) > do_something_quick(); > put_cpu_var(my_var); > > Otherwise if that do_something_quick(); migrates, it may be doing > something it shouldn't be doing!
That is obviously a use case in which this_cpu_xx ops could not be used since we must stay on the same cpu. I think there is still a lot of confusion on your part. The example here shows it.
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