On Wed, 2015-01-14 at 16:43 +0530, Shreyas B. Prabhu wrote:
> LPCR_PECE1 bit controls whether decrementer interrupts are allowed to
> cause exit from power-saving mode. While waking up from winkle, restoring
> LPCR with LPCR_PECE1 set (i.e Decrementer interrupts allowed) can cause
> issue in the following scenario:
>
> - All the threads in a core are offlined. The core enters deep winkle.
> - Spurious interrupt wakes up a thread in the core. Here LPCR is restored
> with LPCR_PECE1 bit set.
> - Since it was a spurious interrupt on a offline thread, the thread clears
> the interrupt and goes back to winkle.
> - Here before the thread executes winkle and puts the core into deep winkle,
> if a decrementer interrupt occurs on any of the sibling threads in the core
> that thread wakes up.
> - Since in offline loop we are flushing interrupt only in case of external
> interrupt, the decrementer interrupt does not get flushed. So at this stage
> the thread is stuck in this is loop of waking up at 0x100 due to decrementer
> interrupt, not flushing the interrupt as only external interrupts get
> flushed,
> entering winkle, waking up at 0x100 again.
>
> Fix this by programming PORE to restore LPCR with LPCR_PECE1 bit
> cleared when waking up from winkle.
That sounds good.
But this makes the third place where we clear LPCR_PECE1, in addition to:
static int fastsleep_loop(struct cpuidle_device *dev,
struct cpuidle_driver *drv,
int index)
{
...
new_lpcr = old_lpcr;
/* Do not exit powersave upon decrementer as we've setup the timer
* offload.
*/
new_lpcr &= ~LPCR_PECE1;
mtspr(SPRN_LPCR, new_lpcr);
And:
static void pnv_smp_cpu_kill_self(void)
{
...
/* We don't want to take decrementer interrupts while we are offline,
* so clear LPCR:PECE1. We keep PECE2 enabled.
*/
mtspr(SPRN_LPCR, mfspr(SPRN_LPCR) & ~(u64)LPCR_PECE1);
So perhaps we can capture that logic in one place somehow?
cheers
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