Re: [PATCH v2] cpuidle: Add 'above' and 'below' idle state metrics
From: Peter Zijlstra <peterz@infradead.org>
Date: 2018-12-10 12:21:22
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linux-doc, lkml
On Mon, Dec 10, 2018 at 12:30:23PM +0100, Rafael J. Wysocki wrote:
From: Rafael J. Wysocki <redacted> Add two new metrics for CPU idle states, "above" and "below", to count the number of times the given state had been asked for (or entered from the kernel's perspective), but the observed idle duration turned out to be too short or too long for it (respectively). These metrics help to estimate the quality of the CPU idle governor in use. Signed-off-by: Rafael J. Wysocki <redacted>
quoted hunk ↗ jump to hunk
@@ -260,6 +262,33 @@ int cpuidle_enter_state(struct cpuidle_d dev->last_residency = (int)diff; dev->states_usage[entered_state].time += dev->last_residency; dev->states_usage[entered_state].usage++; + + if (diff < drv->states[entered_state].target_residency) { + for (i = entered_state - 1; i >= 0; i--) { + if (drv->states[i].disabled || + dev->states_usage[i].disable) + continue; + + /* Shallower states are enabled, so update. */ + dev->states_usage[entered_state].above++; + break; + } + } else if (diff > delay) { + for (i = entered_state + 1; i < drv->state_count; i++) { + if (drv->states[i].disabled || + dev->states_usage[i].disable) + continue; + + /* + * Update if a deeper state would have been a + * better match for the observed idle duration. + */ + if (diff - delay >= drv->states[i].target_residency) + dev->states_usage[entered_state].below++; + + break; + } + }
One question on this; why is this tracked unconditionally? Would not a tracepoint be better?; then there is no overhead in the normal case where nobody gives a crap about these here numbers.