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?
