On 11/28/2011 04:33 AM, Benjamin Herrenschmidt wrote:
> On Thu, 2011-11-17 at 16:58 +0530, Deepthi Dharwar wrote:
>> This patch implements a backhand cpuidle driver for pSeries
>> based on pseries_dedicated_idle_loop and pseries_shared_idle_loop
>> routines. The driver is built only if CONFIG_CPU_IDLE is set. This
>> cpuidle driver uses global registration of idle states and
>> not per-cpu.
>
> .../...
>
>> +#define MAX_IDLE_STATE_COUNT 2
>> +
>> +static int max_cstate = MAX_IDLE_STATE_COUNT - 1;
>
> Why "cstate" ? This isn't an x86 :-)
Sure, I shall change it right away :)
>
>> +static struct cpuidle_device __percpu *pseries_idle_cpuidle_devices;
>
> Shorter name please. pseries_cpuidle_devs is fine.
I ll do so.
>
>> +static struct cpuidle_state *cpuidle_state_table;
>> +
>> +void update_smt_snooze_delay(int snooze)
>> +{
>> + struct cpuidle_driver *drv = cpuidle_get_driver();
>> + if (drv)
>> + drv->states[0].target_residency = snooze;
>> +}
>> +
>> +static inline void idle_loop_prolog(unsigned long *in_purr, ktime_t *kt_before)
>> +{
>> +
>> + *kt_before = ktime_get_real();
>> + *in_purr = mfspr(SPRN_PURR);
>> + /*
>> + * Indicate to the HV that we are idle. Now would be
>> + * a good time to find other work to dispatch.
>> + */
>> + get_lppaca()->idle = 1;
>> + get_lppaca()->donate_dedicated_cpu = 1;
>> +}
>
> I notice that you call this on shared processors as well. The old ocde
> used to not set donate_dedicated_cpu in that case. I assume that's not a
> big deal and that the HV will just ignore it in the shared processor
> case but please add a comment after you've verified it.
>
Yes, the old code does not set donate_dedicated_cpu. But yes I will
try testing it in a shared proc config but also remove this
initialization for shared idle loop.
>> +static inline s64 idle_loop_epilog(unsigned long in_purr, ktime_t kt_before)
>> +{
>> + get_lppaca()->wait_state_cycles += mfspr(SPRN_PURR) - in_purr;
>> + get_lppaca()->donate_dedicated_cpu = 0;
>> + get_lppaca()->idle = 0;
>> +
>> + return ktime_to_us(ktime_sub(ktime_get_real(), kt_before));
>> +}
>> +
>> +
>> +static int snooze_loop(struct cpuidle_device *dev,
>> + struct cpuidle_driver *drv,
>> + int index)
>> +{
>> + unsigned long in_purr;
>> + ktime_t kt_before;
>> +
>> + idle_loop_prolog(&in_purr, &kt_before);
>> +
>> + local_irq_enable();
>> + set_thread_flag(TIF_POLLING_NRFLAG);
>> + while (!need_resched()) {
>> + ppc64_runlatch_off();
>> + HMT_low();
>> + HMT_very_low();
>> + }
>> + HMT_medium();
>> + clear_thread_flag(TIF_POLLING_NRFLAG);
>> + smp_mb();
>> + local_irq_disable();
>> +
>> + dev->last_residency =
>> + (int)idle_loop_epilog(in_purr, kt_before);
>> + return index;
>> +}
>
> So your snooze loop has no timeout, is that handled by the cpuidle
> driver using some kind of timer ? That sounds a lot less efficient than
> passing a max delay to the snooze loop to handle getting into a deeper
> state after a bit of snoozing rather than interrupting etc...
My bad, snooze_loop is essential for a time out. Nope cpuidle
driver doesn't have any timer mechanism. I ll fix it.
Need to add loop for snooze time.
>> +static int dedicated_cede_loop(struct cpuidle_device *dev,
>> + struct cpuidle_driver *drv,
>> + int index)
>> +{
>> + unsigned long in_purr;
>> + ktime_t kt_before;
>> +
>> + idle_loop_prolog(&in_purr, &kt_before);
>> +
>> + ppc64_runlatch_off();
>> + HMT_medium();
>> + cede_processor();
>> +
>> + dev->last_residency =
>> + (int)idle_loop_epilog(in_purr, kt_before);
>> + return index;
>> +}
>> +
>> +static int shared_cede_loop(struct cpuidle_device *dev,
>> + struct cpuidle_driver *drv,
>> + int index)
>> +{
>> + unsigned long in_purr;
>> + ktime_t kt_before;
>> +
>> + idle_loop_prolog(&in_purr, &kt_before);
>> +
>> + /*
>> + * Yield the processor to the hypervisor. We return if
>> + * an external interrupt occurs (which are driven prior
>> + * to returning here) or if a prod occurs from another
>> + * processor. When returning here, external interrupts
>> + * are enabled.
>> + */
>> + cede_processor();
>> +
>> + dev->last_residency =
>> + (int)idle_loop_epilog(in_purr, kt_before);
>> + return index;
>> +}
>> +
>> +/*
>> + * States for dedicated partition case.
>> + */
>> +static struct cpuidle_state dedicated_states[MAX_IDLE_STATE_COUNT] = {
>> + { /* Snooze */
>> + .name = "snooze",
>> + .desc = "snooze",
>> + .flags = CPUIDLE_FLAG_TIME_VALID,
>> + .exit_latency = 0,
>> + .target_residency = 0,
>> + .enter = &snooze_loop },
>> + { /* CEDE */
>> + .name = "CEDE",
>> + .desc = "CEDE",
>> + .flags = CPUIDLE_FLAG_TIME_VALID,
>> + .exit_latency = 1,
>> + .target_residency = 10,
>> + .enter = &dedicated_cede_loop },
>> +};
>> +
>> +/*
>> + * States for shared partition case.
>> + */
>> +static struct cpuidle_state shared_states[MAX_IDLE_STATE_COUNT] = {
>> + { /* Shared Cede */
>> + .name = "Shared Cede",
>> + .desc = "Shared Cede",
>> + .flags = CPUIDLE_FLAG_TIME_VALID,
>> + .exit_latency = 0,
>> + .target_residency = 0,
>> + .enter = &shared_cede_loop },
>> +};
>> +
>> +int pseries_notify_cpuidle_add_cpu(int cpu)
>> +{
>> + struct cpuidle_device *dev =
>> + per_cpu_ptr(pseries_idle_cpuidle_devices, cpu);
>> + if (dev && cpuidle_get_driver()) {
>> + cpuidle_disable_device(dev);
>> + cpuidle_enable_device(dev);
>> + }
>> + return 0;
>> +}
>> +
>> +/*
>> + * pseries_idle_cpuidle_driver_init()
>> + */
>> +static int pseries_idle_cpuidle_driver_init(void)
>> +{
>
> Drop the "idle", those names are too long.
Sure.
>
>> + int cstate;
>
> And use something else than 'cstate', we are among civilized people
> here ;-)
Yes :)
>
>> + struct cpuidle_driver *drv = &pseries_idle_driver;
>> +
>> + drv->state_count = 0;
>> +
>> + for (cstate = 0; cstate < MAX_IDLE_STATE_COUNT; ++cstate) {
>> +
>> + if (cstate > max_cstate)
>> + break;
>> +
>> + /* is the state not enabled? */
>> + if (cpuidle_state_table[cstate].enter == NULL)
>> + continue;
>> +
>> + drv->states[drv->state_count] = /* structure copy */
>> + cpuidle_state_table[cstate];
>> +
>> + if (cpuidle_state_table == dedicated_states)
>> + drv->states[drv->state_count].target_residency =
>> + __get_cpu_var(smt_snooze_delay);
>> +
>> + drv->state_count += 1;
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +/* pseries_idle_devices_uninit(void)
>> + * unregister cpuidle devices and de-allocate memory
>> + */
>> +static void pseries_idle_devices_uninit(void)
>> +{
>> + int i;
>> + struct cpuidle_device *dev;
>> +
>> + for_each_possible_cpu(i) {
>> + dev = per_cpu_ptr(pseries_idle_cpuidle_devices, i);
>> + cpuidle_unregister_device(dev);
>> + }
>> +
>> + free_percpu(pseries_idle_cpuidle_devices);
>> + return;
>> +}
>> +
>> +/* pseries_idle_devices_init()
>> + * allocate, initialize and register cpuidle device
>> + */
>> +static int pseries_idle_devices_init(void)
>> +{
>> + int i;
>> + struct cpuidle_driver *drv = &pseries_idle_driver;
>> + struct cpuidle_device *dev;
>> +
>> + pseries_idle_cpuidle_devices = alloc_percpu(struct cpuidle_device);
>> + if (pseries_idle_cpuidle_devices == NULL)
>> + return -ENOMEM;
>> +
>> + for_each_possible_cpu(i) {
>> + dev = per_cpu_ptr(pseries_idle_cpuidle_devices, i);
>> + dev->state_count = drv->state_count;
>> + dev->cpu = i;
>> + if (cpuidle_register_device(dev)) {
>> + printk(KERN_DEBUG \
>> + "cpuidle_register_device %d failed!\n", i);
>> + return -EIO;
>> + }
>> + }
>> +
>> + return 0;
>> +}
>> +
>> +/*
>> + * pseries_idle_probe()
>> + * Choose state table for shared versus dedicated partition
>> + */
>> +static int pseries_idle_probe(void)
>> +{
>> + if (max_cstate == 0) {
>> + printk(KERN_DEBUG "pseries processor idle disabled.\n");
>> + return -EPERM;
>> + }
>> +
>> + if (!firmware_has_feature(FW_FEATURE_SPLPAR)) {
>> + printk(KERN_DEBUG "Using default idle\n");
>> + return -ENODEV;
>> + }
>
> Don't even printk here, this will happen on all !pseries machines and
> the debug output isn't useful. Also move the check of max-cstate to
> after the splpar test.
I ll move the check above.
> Overall, I quite like these patches, my comments are all pretty minor,
> hopefully the next round should be the one.
Thank you.
>
> Cheers,
> Ben.
>
>
Regards,
Deepthi
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