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4dc2375c1a
Rik reports that he sees an increase in CPU use in one benchmark due to commit 612f1a22f067 "cpuidle: poll_state: Add time limit to poll_idle()" that caused poll_idle() to call local_clock() in every iteration of the loop. Utilization increase generally means more non-idle time with respect to total CPU time (on the average) which implies reduced CPU frequency. Doug reports that limiting the rate of local_clock() invocations in there causes much less power to be drawn during a CPU-intensive parallel workload (with idle states 1 and 2 disabled to enforce more state 0 residency). These two reports together suggest that executing local_clock() on multiple CPUs in parallel at a high rate may cause chips to get hot and trigger thermal/power limits on them to kick in, so reduce the rate of local_clock() invocations in poll_idle() to avoid that issue. Fixes: 612f1a22f067 "cpuidle: poll_state: Add time limit to poll_idle()" Reported-by: Rik van Riel <riel@surriel.com> Reported-by: Doug Smythies <dsmythies@telus.net> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Tested-by: Rik van Riel <riel@surriel.com> Reviewed-by: Rik van Riel <riel@surriel.com>
53 lines
1.2 KiB
C
53 lines
1.2 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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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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break;
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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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