Re: [PATCH 3/3] cpuidle: Select a different state on tick_broadcast_enter() failures
From: Dhruva Gole <hidden>
Date: 2024-08-21 09:52:08
Also in:
linux-pm, lkml
Hi, On May 10, 2015 at 01:19:52 +0200, Rafael J. Wysocki wrote:
From: Rafael J. Wysocki <redacted> If tick_broadcast_enter() fails in cpuidle_enter_state(), try to find another idle state to enter instead of invoking default_idle_call() immediately and returning -EBUSY which should increase the chances of saving some energy in those cases. Signed-off-by: Rafael J. Wysocki <redacted> ---
Found this during code review, hence dug up this old thread again,
quoted hunk ↗ jump to hunk
drivers/cpuidle/cpuidle.c | 20 +++++++++++++++----- 1 file changed, 15 insertions(+), 5 deletions(-) Index: linux-pm/drivers/cpuidle/cpuidle.c ===================================================================--- linux-pm.orig/drivers/cpuidle/cpuidle.c +++ linux-pm/drivers/cpuidle/cpuidle.c@@ -73,7 +73,10 @@ int cpuidle_play_dead(void) } static int find_deepest_state(struct cpuidle_driver *drv, - struct cpuidle_device *dev, bool freeze) + struct cpuidle_device *dev, + unsigned int max_latency, + unsigned int forbidden_flags, + bool freeze) { unsigned int latency_req = 0; int i, ret = freeze ? -1 : CPUIDLE_DRIVER_STATE_START - 1;@@ -83,6 +86,8 @@ static int find_deepest_state(struct cpu struct cpuidle_state_usage *su = &dev->states_usage[i]; if (s->disabled || su->disable || s->exit_latency <= latency_req + || s->exit_latency > max_latency + || (s->flags & forbidden_flags) || (freeze && !s->enter_freeze)) continue;@@ -100,7 +105,7 @@ static int find_deepest_state(struct cpu int cpuidle_find_deepest_state(struct cpuidle_driver *drv, struct cpuidle_device *dev) { - return find_deepest_state(drv, dev, false); + return find_deepest_state(drv, dev, UINT_MAX, 0, false); } static void enter_freeze_proper(struct cpuidle_driver *drv,@@ -139,7 +144,7 @@ int cpuidle_enter_freeze(struct cpuidle_ * that interrupts won't be enabled when it exits and allows the tick to * be frozen safely. */ - index = find_deepest_state(drv, dev, true); + index = find_deepest_state(drv, dev, UINT_MAX, 0, true); if (index >= 0) enter_freeze_proper(drv, dev, index);@@ -168,8 +173,13 @@ int cpuidle_enter_state(struct cpuidle_d * CPU as a broadcast timer, this call may fail if it is not available. */ if (broadcast && tick_broadcast_enter()) { - default_idle_call(); - return -EBUSY; + index = find_deepest_state(drv, dev, target_state->exit_latency, + CPUIDLE_FLAG_TIMER_STOP, false); + if (index < 0) {
Would this condition ever meet? If you see, the ret inside find_deepest_state is always starting with a 0 and then nobody is ever really making it negative again. So the func either returns a 0 or some positive value right? Since nobody has probably raised an issue about this in 9 years, is this basically dead code inside the if? Let me know what needs to be done here, I'd be happy to patch this up.
+ default_idle_call(); + return -EBUSY; + } + target_state = &drv->states[index]; } /* Take note of the planned idle state. */
-- Best regards, Dhruva Gole [off-list ref]