Messages in this thread | | | Date | Mon, 15 Jun 2020 20:40:41 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH][RFC] PM / s2idle: Clear _TIF_POLLING_NRFLAG before suspend to idle |
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On Tue, Jun 16, 2020 at 01:36:11AM +0800, Chen Yu wrote: > Suspend to idle was found to not work on Goldmont CPU recently. > And the issue was triggered due to: > > 1. On Goldmont the CPU in idle can only be woken up via IPIs, > not POLL mode: > Commit 08e237fa56a1 ("x86/cpu: Add workaround for MONITOR > instruction erratum on Goldmont based CPUs") > 2. When the CPU is entering suspend to idle process, the > _TIF_POLLING_NRFLAG is kept on. > 3. Commit b2a02fc43a1f ("smp: Optimize send_call_function_single_ipi()") > makes use of _TIF_POLLING_NRFLAG to avoid sending IPIs to > idle CPUs. > 4. As a result, some IPIs related functions might not work > well during suspend to idle on Goldmont. For example, one > suspected victim: > tick_unfreeze() -> timekeeping_resume() -> hrtimers_resume() > -> clock_was_set() -> on_each_cpu() might wait forever, > because the IPIs will not be sent to the CPUs which are > sleeping with _TIF_POLLING_NRFLAG set, and Goldmont CPU > could not be woken up by only setting _TIF_NEED_RESCHED > on the monitor address.
*sigh*... just what we need.
> @@ -186,8 +187,10 @@ int cpuidle_enter_s2idle(struct cpuidle_driver *drv, struct cpuidle_device *dev) > * be frozen safely. > */ > index = find_deepest_state(drv, dev, U64_MAX, 0, true); > - if (index > 0) > + if (index > 0) { > + __current_clr_polling(); > enter_s2idle_proper(drv, dev, index); > + } > > return index; > }
So how is that commit 08e237fa56a1 not suffient? That makes mwait_idle_with_hints() DTRT for this 'functionally challenged' piece of hardware.
AFAICT intel_enter_s2idle() uses mwait_idle_with_hints().
What am I missing?
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