Messages in this thread | | | Date | Thu, 30 Apr 2020 17:18:15 +0100 | From | Will Deacon <> | Subject | Re: [PATCH] arm64: perf_event: Fix time_offset for arch timer |
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On Thu, Apr 30, 2020 at 06:04:36PM +0200, Peter Zijlstra wrote: > On Thu, Apr 30, 2020 at 04:29:23PM +0100, Marc Zyngier wrote: > > > I wonder if we could/should make __sched_clock_offset available even when > > CONFIG_HAVE_UNSTABLE_SCHED_CLOCK isn't defined. It feels like it would > > help with this particular can or worm... > > Errrgh. __sched_clock_offset is only needed on x86 because we transition > from one clock device to another on boot. It really shouldn't exist on > anything sane.
I think we still transition from jiffies on arm64, because we don't register with sched_clock until the timer driver probes. Marc, is that right?
> Let me try and understand your particular problem better.
I think the long and short of it is that userspace needs a way to convert the raw counter cycles into a ns value that can be compared against values coming out of sched_clock. To do this accurately, I think it needs the cycles value at the point when sched_clock was initialised.
Will
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