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 3D376C83F1B for ; Thu, 10 Jul 2025 15:04:48 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id D1EA910E8EC; Thu, 10 Jul 2025 15:04:47 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=intel.com header.i=@intel.com header.b="hVf6KCpU"; dkim-atps=neutral Received: from mgamail.intel.com (mgamail.intel.com [198.175.65.21]) by gabe.freedesktop.org (Postfix) with ESMTPS id 1997410E8EC for ; Thu, 10 Jul 2025 15:04:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=intel.com; i=@intel.com; q=dns/txt; s=Intel; t=1752159886; x=1783695886; h=date:from:to:cc:subject:message-id:references: mime-version:content-transfer-encoding:in-reply-to; bh=ymzN0OQOmMbxqP3l5Qj3gim/nnQL5NzNUtbMLt/hT5M=; b=hVf6KCpUlB5/19BGvFxFRuWsgzdCHov7GsW/i5+WvclsS22+okt2E1a2 uKraFSCFHmXF12T+u2997/jrw9boPNtU0VXCkwlbR3CdMOafpYy2Zl+/I Qds1IrDpyaQD/vLkBEgBk/VYVvgtwqwEZG3sZh3GFTTNeSOAgiNvR5Egv daL3tK4Nq6dKha0dfwvIFmmXqYmeI8N7wY+Ew9FWvOIWCdabhlujx0oT/ Kc/zj7hlxvjxTBx+yAYOnnbJP71axT6Eq6G5GAb9ChEHXgBigM9Hx1jkX j4uzE+DS5wuzfQTAmvzvAWrkmVlVlz6Lxr0LiFi/jSYsP3f7StsaVMPYi w==; X-CSE-ConnectionGUID: l2jT5AmJTzmP+OIMJ/Oh4Q== X-CSE-MsgGUID: Tn62ePOfR/KVy9NZn2D8zw== X-IronPort-AV: E=McAfee;i="6800,10657,11490"; a="54321419" X-IronPort-AV: E=Sophos;i="6.16,300,1744095600"; d="scan'208";a="54321419" Received: from orviesa005.jf.intel.com ([10.64.159.145]) by orvoesa113.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 10 Jul 2025 08:04:45 -0700 X-CSE-ConnectionGUID: h/ZtnT3DRsKiCm/16mmIrw== X-CSE-MsgGUID: 2rW0fFz/S4q4uWAxsl3Jlg== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="6.16,300,1744095600"; d="scan'208";a="161805873" Received: from klitkey1-mobl1.ger.corp.intel.com (HELO stinkbox) ([10.245.244.160]) by orviesa005.jf.intel.com with SMTP; 10 Jul 2025 08:04:43 -0700 Received: by stinkbox (sSMTP sendmail emulation); Thu, 10 Jul 2025 18:04:42 +0300 Date: Thu, 10 Jul 2025 18:04:42 +0300 From: Ville =?iso-8859-1?Q?Syrj=E4l=E4?= To: Sebastian Andrzej Siewior Cc: Ben Hutchings , linux-rt-users@vger.kernel.org, intel-gfx@lists.freedesktop.org, Debian kernel maintainers Subject: Re: PREEMPT_RT vs i915 Message-ID: References: <7c42fe5a6158445e150e7d63991767e44fc36d3d.camel@decadent.org.uk> <20250709194443.lkevdn6m@linutronix.de> <20250710064136.rur6FoOU@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20250710064136.rur6FoOU@linutronix.de> 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 Thu, Jul 10, 2025 at 08:41:36AM +0200, Sebastian Andrzej Siewior wrote: > On 2025-07-09 23:09:22 [+0300], Ville Syrjälä wrote: > > On Wed, Jul 09, 2025 at 09:44:43PM +0200, Sebastian Andrzej Siewior wrote: > > > On 2025-07-09 20:30:26 [+0300], Ville Syrjälä wrote: > > > > > > > > > > It seems like the critical uncore lock is currently held in a lot of > > > > > places and potentially for a long time. > > > > > > > > It shouldn't be held for that long. I think it should just be > > > > a raw spinlock. > > > > > > What about I resubmit the series and we look again? I don't think the > > > lock should be made raw just to be done with it. > > > > Until someone actually does the work to confirm the thing is working > > reliably there's no point in posting anything. > > Well it works on my machine and this machine dose not pass the code > paths that I patch. > > Every patch made was done because someone reported an error/ warning and > confirmed afterwards that the patch fixes it for them and they can use > the machine and don't observe anything. > > > And IIRC the other remaining problem with RT was the spinlocks used > > inside tracepoints (which is uncore lock, and probably some vblank > > locks). So that too needs some kind of solution because it's going to > > very hard to debug the timing sensitive parts without the tracepoints. > > no, not just that. Making the lock raw led to latency spikes in simple > spikes and I just disabled trace points. It could be worked around by > taking the lock if the tracepoint is enabled and then invoking the > tracepoint unconditionally and not taking the lock anymore. Steven made > a suggestion a while ago how to put this in macro as far as I remember. When this was last discussed I suggested that there should be a versions of the tracepoint macros that do the sampling outside the lock, but that wasn't deemed acceptable for whatever reason. I don't even know why the current macros are doing the sampling while holding the lock... -- Ville Syrjälä Intel