On 2024-06-14 13:19:25 [+0100], Tvrtko Ursulin wrote: > > So the question is why do you need to know if the context is atomic? > > The only impact is avoiding disabling preemption. Is it that important > > to avoid it? > > If so would cant_migrate() work? It requires CONFIG_DEBUG_ATOMIC_SLEEP=y > > to do the trick. > > ... catching misuse of atomic wait helpers step 2 - are you calling it from > a non-atomic context without the real need. So should use the non-atomic > helper instead. > > When i915 development was very active and with a lot of contributors it was > beneficial to catch these things which code review would easily miss. > > Now that the pace is much, much slower, it is probably not very important. > So this patch is acceptable for what I am concerned and: > > Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxx> > > Actually please also add the PREEMPT_RT angle to the comment above > _WAIT_FOR_ATOMIC_CHECK. Sometimes lines change and git blame makes it hard > to find the commit text. Do you want me the repost the series? Are the bots happy enough? I have the following as far this patch: ------->8-------------- 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@xxxxxxxxxx> Link: https://lore.kernel.org/all/20211006164628.s2mtsdd2jdbfyf7g@xxxxxxxxxxxxx/ Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx> --- drivers/gpu/drm/i915/i915_utils.h | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_utils.h b/drivers/gpu/drm/i915/i915_utils.h index 06ec6ceb61d57..f0d3c5cdc1b1b 100644 --- a/drivers/gpu/drm/i915/i915_utils.h +++ b/drivers/gpu/drm/i915/i915_utils.h @@ -273,8 +273,13 @@ wait_remaining_ms_from_jiffies(unsigned long timestamp_jiffies, int to_wait_ms) (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 warnings + * which don't occur otherwise and is therefore 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) > Regards, > > Tvrtko Sebastian
