From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id AA9A7C83F22 for ; Tue, 15 Jul 2025 17:55:03 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id E0A3A10E385; Tue, 15 Jul 2025 17:55:02 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=intel.com header.i=@intel.com header.b="Cbn7vG5f"; dkim-atps=neutral Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.13]) by gabe.freedesktop.org (Postfix) with ESMTPS id EFA8410E234; Tue, 15 Jul 2025 17:55:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1752602100; x=1784138100; h=date:from:to:cc:subject:message-id:references: mime-version:content-transfer-encoding:in-reply-to; bh=WX8NvVu8eRxRiV8malCikl9drxvPW3hDfX2d94hGY40=; b=Cbn7vG5fCNteykX5Ag36tK5mY3yTtXD3meKfLmSCEhi03D9QuFZrEb3G jGiXoEABgr/RMkKlXw6YpeyFSEata8wfZOtcCJG9Fj5Vqz18ve1sbEbhW P5i3HZPhGNgc20cUQlBxB/GC8KrNxjKGGNdPm8tXDMq7In1qdx+m1Xmyy 48ipjzRW95iSc9RLf8fCfnl3zGBugH3aMsYHE5uHCS1oUZSm2Zq4rLbxu sac0T2J4DzX9QvetDtqlOq1RQSSI4Wsld2EtqY6HfMo7VLeq6JWTxRzWs wu/RZrq1T8Fyipf5KWSDyZhVrdsEl+EEOuEjh9/cdceIvf6mY0QY9ZGdW Q==; X-CSE-ConnectionGUID: ImDfF9XXSVmDcRruTbN5Gw== X-CSE-MsgGUID: lMq+p4hkRuK+exAOxfWONg== X-IronPort-AV: E=McAfee;i="6800,10657,11493"; a="65900850" X-IronPort-AV: E=Sophos;i="6.16,313,1744095600"; d="scan'208";a="65900850" Received: from orviesa005.jf.intel.com ([10.64.159.145]) by orvoesa105.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 15 Jul 2025 10:54:59 -0700 X-CSE-ConnectionGUID: nzSpAu4HQMqfiVCUC1P70A== X-CSE-MsgGUID: nydGvjKuSEWSA+qpx7y6bg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.16,313,1744095600"; d="scan'208";a="162930490" Received: from fpallare-mobl4.ger.corp.intel.com (HELO stinkbox) ([10.245.245.63]) by orviesa005.jf.intel.com with SMTP; 15 Jul 2025 10:54:56 -0700 Received: by stinkbox (sSMTP sendmail emulation); Tue, 15 Jul 2025 20:54:54 +0300 Date: Tue, 15 Jul 2025 20:54:54 +0300 From: Ville =?iso-8859-1?Q?Syrj=E4l=E4?= To: Maarten Lankhorst Cc: Sebastian Andrzej Siewior , intel-gfx@lists.freedesktop.org, intel-xe@lists.freedesktop.org, Jani Nikula , Joonas Lahtinen , Rodrigo Vivi , Thomas Gleixner , Tvrtko Ursulin , Scott Oehrlein , Ben Hutchings , Tvrtko Ursulin , Luca Abeni , Steven Rostedt Subject: Re: [PATCH v4 4/9] drm/i915: Disable tracing points on PREEMPT_RT Message-ID: References: <20250714153954.629393-1-bigeasy@linutronix.de> <20250714153954.629393-5-bigeasy@linutronix.de> <272f743e-15f7-4dc0-a6c0-08cd60ca6cc2@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <272f743e-15f7-4dc0-a6c0-08cd60ca6cc2@linux.intel.com> X-Patchwork-Hint: comment X-BeenThere: intel-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Intel graphics driver community testing & development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: intel-gfx-bounces@lists.freedesktop.org Sender: "Intel-gfx" 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 > > Reported-by: Luca Abeni > > Cc: Steven Rostedt > > Signed-off-by: Sebastian Andrzej Siewior > > --- > > 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 > > #include > > #include > > 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 > > #include > > #include > > 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 -- Ville Syrjälä Intel