On Tue, Jul 15, 2025 at 10:01:45AM +0200, Maarten Lankhorst wrote: > Hey, > > I believe the platforms that require spinlocks for reading registers all > predate Xe, > so it should be possible to enable tracepoints on Xe. > > I do see there is still a path there that takes locks, through > intel_crtc_get_vblank_counter -> drm_crtc_accurate_vblank_count(). > > I would recommend changing intel_crtc_get_vblank_counter to use > drm_vblank_count(), > which doesn't take locks. > > This reduces vblank accuracy slightly on old platforms and gen11+ DSI, but I > would say for most usecases it has the same accuracy,
The non-accurate version is completely useless here. So NAK. > with the benefit of keeping tracepoints enabled. The only users for > intel_crtc_get_vblank_counter() are debug functions. > > With that change, something like: > "#if defined(CONFIG_PREEMPT_RT) && defined(I915) && !defined(NOTRACE)" > > would disable tracepoints only on i915. > > Kind regards, > ~Maarten > > Den 2025-07-14 kl. 17:39, skrev Sebastian Andrzej Siewior: > > Luca Abeni reported this: > > | BUG: scheduling while atomic: kworker/u8:2/15203/0x00000003 > > | CPU: 1 PID: 15203 Comm: kworker/u8:2 Not tainted 4.19.1-rt3 #10 > > | Call Trace: > > | rt_spin_lock+0x3f/0x50 > > | gen6_read32+0x45/0x1d0 [i915] > > | g4x_get_vblank_counter+0x36/0x40 [i915] > > | trace_event_raw_event_i915_pipe_update_start+0x7d/0xf0 [i915] > > > > The tracing events use trace_intel_pipe_update_start() among other events > > use functions acquire spinlock_t locks which are transformed into > > sleeping locks on PREEMPT_RT. A few trace points use > > intel_get_crtc_scanline(), others use ->get_vblank_counter() wich also > > might acquire a sleeping locks on PREEMPT_RT. > > At the time the arguments are evaluated within trace point, preemption > > is disabled and so the locks must not be acquired on PREEMPT_RT. > > > > Based on this I don't see any other way than disable trace points on > > PREMPT_RT. > > > > Acked-by: Tvrtko Ursulin <tvrtko.ursu...@igalia.com> > > Reported-by: Luca Abeni <lucab...@gmail.com> > > Cc: Steven Rostedt <rost...@goodmis.org> > > Signed-off-by: Sebastian Andrzej Siewior <bige...@linutronix.de> > > --- > > drivers/gpu/drm/i915/display/intel_display_trace.h | 4 ++++ > > drivers/gpu/drm/i915/i915_trace.h | 4 ++++ > > drivers/gpu/drm/i915/intel_uncore_trace.h | 4 ++++ > > 3 files changed, 12 insertions(+) > > > > diff --git a/drivers/gpu/drm/i915/display/intel_display_trace.h > > b/drivers/gpu/drm/i915/display/intel_display_trace.h > > index 27ebc32cb61a5..a519d94700c36 100644 > > --- a/drivers/gpu/drm/i915/display/intel_display_trace.h > > +++ b/drivers/gpu/drm/i915/display/intel_display_trace.h > > @@ -13,6 +13,10 @@ > > #if !defined(__INTEL_DISPLAY_TRACE_H__) || defined(TRACE_HEADER_MULTI_READ) > > #define __INTEL_DISPLAY_TRACE_H__ > > > > +#if defined(CONFIG_PREEMPT_RT) && !defined(NOTRACE) > > +#define NOTRACE > > +#endif > > + > > #include <linux/string.h> > > #include <linux/string_helpers.h> > > #include <linux/types.h> > > diff --git a/drivers/gpu/drm/i915/i915_trace.h > > b/drivers/gpu/drm/i915/i915_trace.h > > index 7ed41ce9b7085..6b87ef6005c69 100644 > > --- a/drivers/gpu/drm/i915/i915_trace.h > > +++ b/drivers/gpu/drm/i915/i915_trace.h > > @@ -6,6 +6,10 @@ > > #if !defined(_I915_TRACE_H_) || defined(TRACE_HEADER_MULTI_READ) > > #define _I915_TRACE_H_ > > > > +#if defined(CONFIG_PREEMPT_RT) && !defined(NOTRACE) > > +#define NOTRACE > > +#endif > > + > > #include <linux/stringify.h> > > #include <linux/types.h> > > #include <linux/tracepoint.h> > > diff --git a/drivers/gpu/drm/i915/intel_uncore_trace.h > > b/drivers/gpu/drm/i915/intel_uncore_trace.h > > index f13ff71edf2db..3c67e267fb602 100644 > > --- a/drivers/gpu/drm/i915/intel_uncore_trace.h > > +++ b/drivers/gpu/drm/i915/intel_uncore_trace.h > > @@ -7,6 +7,10 @@ > > #if !defined(__INTEL_UNCORE_TRACE_H__) || defined(TRACE_HEADER_MULTI_READ) > > #define __INTEL_UNCORE_TRACE_H__ > > > > +#if defined(CONFIG_PREEMPT_RT) && !defined(NOTRACE) > > +#define NOTRACE > > +#endif > > + > > #include "i915_reg_defs.h" > > > > #include <linux/types.h> -- Ville Syrjälä Intel
