On Mon, 6 Jul 2015, Sudeep Holla wrote:
> On 05/07/15 21:53, Thomas Gleixner wrote:
> > If no broadcast device is installed and the cpu local timers stop in
> > deeper idle states, then there is currently nothing telling the idle
> > code that it should not go into deep idle states, so the timers stop
> > and nothing wakes up the cpus.
> >
> > Make the broadcast_enter/exit() functions independent of the
> > configuration options and always check on enter:
> >
> > - whether the cpu local device is affected by idle states
> > - whether a broadcast device is available
> >
> > This covers all possible config combinations including
> > CONFIG_BROADCAST=n.
> >
> > Reported-by: Sudeep Holla <[email protected]>
>
> Sorry for the delay, took a while testing few configuration:
>
> +--------------+--------+--------------+--------------------+
> | Configs | PERIOD | HRTimers+NOHz|Cmdline(HR+NoHZ=off)|
> +--------------+--------+--------------+--------------------+
> | UP w/o H/W BC| OK | OK | OK |
> +--------------+--------+--------------+--------------------+
> | UP w/ H/W BC | OK | OK | OK |
> +--------------+--------+--------------+--------------------+
> |SMP w/o H/W BC| OK* | OK | Not OK(**) |
> +--------------+--------+--------------+--------------------+
> |SMP w/ H/W BC | OK | OK | OK |
> +--------------+--------+--------------+--------------------+
>
> H/W BC - Hardware Broadcast Timer source
>
> (*) None of the CPUs enters deeper idle states losing local timers
>
> (**)SMP build without Hardware Broadcast Timer source(i.e. one cpu is
> the broadcast source) with HRTimers+NOHz configs but disabled in cmdline
> fails to boot.
That's using the hrtimer broadcast mechanism, right?
> On connecting debugger, I found all the cpus are in
> shallow idle state(i.e. WFI in ARM) but with interrupts disabled.
And that means?
> I am not really keen on the failing configuration. We have never tested
> that before, though I found it working with CPUIdle disabled.
Well, we should figure out what happens while we are at it before
everything gets paged out again.
In the case of CONFIG_NOHZ=n and CONFIG_HIGHRES=n the broadcast
hrtimer is not compiled as it depends on CONFIG_TICK_ONESHOT, so it
works via the bc.evtdev == NULL check.
With either option enabled CONFIG_TICK_ONESHOT gets set, so the
broadcast timer gets installed but somehow does not work proper if
nohz and highres are disabled on the kernel command line.
Thanks,
tglx
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