On a Intel G4400 "Skylake" with kernel 4.9.47-rt37 I get a
reproducible latency spike (>200us) when the screen goes to standby.
The display is connected to the onboard DVI connector. The same thing
works fine on an older Ivy Bridge CPU. To trigger the spike when in
Xorg I use:
xset dpms force off
After setting the options below for the i915 kernel module I was no
longer able to reproduce the spikes:
- enable_rc6=0
- enable_dc=0
- disable_power_well=0
Below an excerpt of the trace before the latency occurred:
Xorg-1385 1....11. 15579034us : pin_current_cpu <-migrate_disable
Xorg-1385 1.....11 15579035us : rt_spin_unlock <-gen9_read32
Xorg-1385 1.....11 15579035us : migrate_enable <-rt_spin_unlock
Xorg-1385 1....11. 15579035us : unpin_current_cpu <-migrate_enable
Xorg-1385 1....... 15579035us : gen9_read32 <-gen9_set_dc_state
Xorg-1385 1....... 15579035us : rt_spin_lock <-gen9_read32
Xorg-1385 1....... 15579035us : migrate_disable <-rt_spin_lock
Xorg-1385 1....11. 15579035us : pin_current_cpu <-migrate_disable
Xorg-1385 1.....11 15579035us : rt_spin_unlock <-gen9_read32
Xorg-1385 1.....11 15579035us : migrate_enable <-rt_spin_unlock
Xorg-1385 1....11. 15579035us : unpin_current_cpu <-migrate_enable
Xorg-1385 1....... 15579035us : gen9_read32 <-gen9_set_dc_state
Xorg-1385 1....... 15579036us : rt_spin_lock <-gen9_read32
Xorg-1385 1....... 15579036us : migrate_disable <-rt_spin_lock
Xorg-1385 1....11. 15579036us!: pin_current_cpu <-migrate_disable
Xorg-1385 1d....11 15579425us : smp_apic_timer_interrupt
<-apic_timer_interrupt
Xorg-1385 1d....11 15579425us : irq_enter <-smp_apic_timer_interrupt
Xorg-1385 1d....11 15579425us : rcu_irq_enter <-irq_enter
Xorg-1385 1d..h.11 15579425us : exit_idle <-smp_apic_timer_interrupt
Christoph
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