* Gautham R Shenoy <e...@linux.vnet.ibm.com> [2018-07-03 10:54:16]:
> From: "Gautham R. Shenoy" <e...@linux.vnet.ibm.com>
>
> In the situations where snooze is the only cpuidle state due to
> firmware not exposing any platform idle states, the idle CPUs will
> remain in snooze for a long time with interrupts disabled causing the
> Hard-lockup detector to complain.
snooze_loop() will spin in SMT low priority with interrupt enabled. We
have local_irq_enable() before we get into the snooze loop.
Since this is a polling state, we should wakeup without an interrupt
and hence we set TIF_POLLING_NRFLAG as well.
> watchdog: CPU 51 detected hard LOCKUP on other CPUs 59
> watchdog: CPU 51 TB:535296107736, last SMP heartbeat TB:527472229239 (15281ms
> ago)
> watchdog: CPU 59 Hard LOCKUP
> watchdog: CPU 59 TB:535296252849, last heartbeat TB:526554725466 (17073ms ago)
hmm.. not sure why watchdog will complain, maybe something more is
going on.
> Fix this by adding CPUIDLE_FLAG_POLLING flag to the state, so that the
> cpuidle governor will do the right thing, such as not stopping the
> tick if it is going to put the idle cpu to snooze.
>
> Reported-by: Akshay Adiga <akshay.ad...@linux.vnet.ibm.com>
> Cc: Nicholas Piggin <npig...@gmail.com>
> Signed-off-by: Gautham R. Shenoy <e...@linux.vnet.ibm.com>
> ---
> drivers/cpuidle/cpuidle-powernv.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/drivers/cpuidle/cpuidle-powernv.c
> b/drivers/cpuidle/cpuidle-powernv.c
> index d29e4f0..b73041b 100644
> --- a/drivers/cpuidle/cpuidle-powernv.c
> +++ b/drivers/cpuidle/cpuidle-powernv.c
> @@ -156,6 +156,7 @@ static int stop_loop(struct cpuidle_device *dev,
> { /* Snooze */
> .name = "snooze",
> .desc = "snooze",
> + .flags = CPUIDLE_FLAG_POLLING,
> .exit_latency = 0,
> .target_residency = 0,
> .enter = snooze_loop },
Adding the CPUIDLE_FLAG_POLLING is good and enables more optimization.
But the reason that we spin with interrupt disabled does not seem
right.
--Vaidy
