27ab8f1648
[ Upstream commit 5f26bdceb9c0a5e6c696aa2899d077cd3ae93413 ]
If the CPU exits the "polling" state due to the time limit in the
loop in poll_idle(), this is not a real wakeup and it just means
that the "polling" state selection was not adequate. The governor
mispredicted short idle duration, but had a more suitable state been
selected, the CPU might have spent more time in it. In fact, there
is no reason to expect that there would have been a wakeup event
earlier than the next timer in that case.
Handling such cases as regular wakeups in menu_update() may cause the
menu governor to make suboptimal decisions going forward, but ignoring
them altogether would not be correct either, because every time
menu_select() is invoked, it makes a separate new attempt to predict
the idle duration taking distinct time to the closest timer event as
input and the outcomes of all those attempts should be recorded.
For this reason, make menu_update() always assume that if the
"polling" state was exited due to the time limit, the next proper
wakeup event for the CPU would be the next timer event (not
including the tick).
Fixes: a37b969a61 "cpuidle: poll_state: Add time limit to poll_idle()"
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
57 lines
1.3 KiB
C
57 lines
1.3 KiB
C
/*
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* poll_state.c - Polling idle state
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*
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* This file is released under the GPLv2.
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*/
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#include <linux/cpuidle.h>
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#include <linux/sched.h>
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#include <linux/sched/clock.h>
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#include <linux/sched/idle.h>
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#define POLL_IDLE_TIME_LIMIT (TICK_NSEC / 16)
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#define POLL_IDLE_RELAX_COUNT 200
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static int __cpuidle poll_idle(struct cpuidle_device *dev,
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struct cpuidle_driver *drv, int index)
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{
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u64 time_start = local_clock();
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dev->poll_time_limit = false;
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local_irq_enable();
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if (!current_set_polling_and_test()) {
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unsigned int loop_count = 0;
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while (!need_resched()) {
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cpu_relax();
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if (loop_count++ < POLL_IDLE_RELAX_COUNT)
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continue;
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loop_count = 0;
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if (local_clock() - time_start > POLL_IDLE_TIME_LIMIT) {
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dev->poll_time_limit = true;
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break;
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}
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}
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}
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current_clr_polling();
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return index;
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}
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void cpuidle_poll_state_init(struct cpuidle_driver *drv)
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{
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struct cpuidle_state *state = &drv->states[0];
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snprintf(state->name, CPUIDLE_NAME_LEN, "POLL");
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snprintf(state->desc, CPUIDLE_DESC_LEN, "CPUIDLE CORE POLL IDLE");
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state->exit_latency = 0;
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state->target_residency = 0;
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state->power_usage = -1;
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state->enter = poll_idle;
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state->disabled = false;
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state->flags = CPUIDLE_FLAG_POLLING;
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}
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EXPORT_SYMBOL_GPL(cpuidle_poll_state_init);
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