Messages in this thread | | | From | David Howells <> | Subject | Re: [RFC patch 08/18] cnt32_to_63 should use smp_rmb() | Date | Fri, 07 Nov 2008 11:03:35 +0000 |
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Nicolas Pitre <nico@cam.org> wrote:
> > I mean, the darned thing is called from sched_clock(), which can be > > concurrently called on separate CPUs and which can be called from > > interrupt context (with an arbitrary nesting level!) while it was running > > in process context. > > Yes! And this is so on *purpose*. Please take some time to read the > comment that goes along with it, and if you're still not convinced then > look for those explanation emails I've already posted.
I agree with Nicolas on this. It's abominably clever, but I think he's right.
The one place I remain unconvinced is over the issue of preemption of a process that is in the middle of cnt32_to_63(), where if the preempted process is asleep for long enough, I think it can wind time backwards when it resumes, but that's not a problem for the one place I want to use it (sched_clock()) because that is (almost) always called with preemption disabled in one way or another.
The one place it isn't is a debugging case that I'm not too worried about.
> > /* > > * Caller must provide locking to protect *caller_state > > */ > > NO! This is meant to be LOCK FREE!
Absolutely.
David
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