From: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Date: Mon, 25 Oct 2021 15:05:18 +0200 Subject: [PATCH 3/8] drm/i915: Don't check for atomic context on PREEMPT_RT The !in_atomic() check in _wait_for_atomic() triggers on PREEMPT_RT because the uncore::lock is a spinlock_t and does not disable preemption or interrupts. Changing the uncore:lock to a raw_spinlock_t doubles the worst case latency on an otherwise idle testbox during testing. Ignore _WAIT_FOR_ATOMIC_CHECK() on PREEMPT_RT. Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com> Link: https://lore.kernel.org/all/20211006164628.s2mtsdd2jdbfyf7g@linutronix.de/ Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> --- drivers/gpu/drm/i915/i915_utils.h | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) @ drivers/gpu/drm/i915/i915_utils.h:276 @ wait_remaining_ms_from_jiffies(unsigned (Wmax)) #define wait_for(COND, MS) _wait_for((COND), (MS) * 1000, 10, 1000) -/* If CONFIG_PREEMPT_COUNT is disabled, in_atomic() always reports false. */ -#if defined(CONFIG_DRM_I915_DEBUG) && defined(CONFIG_PREEMPT_COUNT) +/* + * If CONFIG_PREEMPT_COUNT is disabled, in_atomic() always reports false. + * On PREEMPT_RT the context isn't becoming atomic because it is used in an + * interrupt handler or because a spinlock_t is acquired. This leads to + * warnings which don't occur otherwise and therefore the check is disabled. + */ +#if defined(CONFIG_DRM_I915_DEBUG) && defined(CONFIG_PREEMPT_COUNT) && !defined(CONFIG_PREEMPT_RT) # define _WAIT_FOR_ATOMIC_CHECK(ATOMIC) WARN_ON_ONCE((ATOMIC) && !in_atomic()) #else # define _WAIT_FOR_ATOMIC_CHECK(ATOMIC) do { } while (0)