Messages in this thread | | | Date | Tue, 20 Sep 2011 15:51:32 +0200 (CEST) | From | Thomas Gleixner <> | 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, 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_*()". > > What's the latency hit on those very few locations if we simply put our > collective foot down and not support a preemptable version of this_cpu_*()? > "Yes, you *could* preempt here, but for our collective sanity that's not > supported"...
Full ack.
> > All this_cpu*() code, except the funny named ones, should make sure > > preemption is disabled, otherwise give a nasty warning. As that is > > usually a bug if you are using a per cpu variable and can migrate away. > > The next reference to that value may be incorrect. > > You get a much prettier diffstat if you just nuke the funny named ones. ;)
Along with the maze of completely unused incarnations.
> But of course it's early morning and I'm still caffeine-deficient and probably > overlooking some crucial use case. ;)
I doubt that.
Thanks,
tglx
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