Re: [RFC][PATCH 0/5] Introduce checks for preemptable code for this_cpu_read/write()

Christoph Lameter
2011-09-20T14:57:37Z

On Tue, 20 Sep 2011, Valdis.Kletnieks@vt.edu wrote:

> On Mon, 19 Sep 2011 23:06:17 EDT, Steven Rostedt said:
>
> > It is really confusing to know which version to use. I'm confused by the
> > this_cpu_*() compared with __this_cpu_*(). I'm guessing that most places
> > should use __this_cpu*(). But really this_cpu() should be the default,
> > and the places that can have it outside of preemption should have
> > another name. Maybe use the raw_this_cpu() or safe_this_cpu(), as there
> > is an irqsafe_this_cpu(). Maybe make a preemptsafe_cpu_*(). There should
> > only be a very few locations that are OK to have preemption enabled when
> > calling the this_cpu() code. Lets have those have the funny names and
> > not be the default "this_cpu_*()".

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.