From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from galois.linutronix.de (Galois.linutronix.de [193.142.43.55]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 15646233704; Tue, 28 Oct 2025 13:58:00 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=193.142.43.55 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761659882; cv=none; b=NUwchYoQyseurlASFc/WA5/htFB9tegTIIudTBC6v5rbTVxIxv8vK+fdM8hoHTzhgYAg0eaNfTgdmjvFdW9aKK8W7QO0+DyTwETt+/cuwwvXhAs80aARB6x75bflgdZkz8VoIxjlnVBownAa2a0efGj7xKHV2bkmfqNVdExy3lI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1761659882; c=relaxed/simple; bh=jwhkSKyIAKFcKFKcHbcE5yLIWsbhuzQegvHxTtFBzts=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=lsNevQpHhVkWayBsMytRCOv3xoSij57c2PxqQ4EBFwkjXywl7mEGafOquHSSE17U2VuVfp2WmFDVwo5YDRLFYl/M9iXSsRbagXFAD2LfO4yDBQ5prFHBi4Igx7INtBCPVrYvG5xVIdiGpmm+3BBpHDzc2NlxrxGnOxuQ86rDWek= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de; spf=pass smtp.mailfrom=linutronix.de; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=uOeqyrTx; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b=ZyyuACtX; arc=none smtp.client-ip=193.142.43.55 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linutronix.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linutronix.de Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="uOeqyrTx"; dkim=permerror (0-bit key) header.d=linutronix.de header.i=@linutronix.de header.b="ZyyuACtX" Date: Tue, 28 Oct 2025 14:57:56 +0100 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1761659878; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=q4sSQfkLnUOR6EYFSrWyzoEwtf3zqvnnuhYr4uBXt5w=; b=uOeqyrTxLDYiEMrmWVSQnhrBNLXvhfmhLJnXro8s8e/5+TaBX3e5hHYQ6wrfnnpA/D+2Br VepBCLLZ3mf2vpT0Gz3Vb2syn2mtMHOQBa2es2M8TlOQbwY7PIJcir1YnIN+/U8BCAMrWA edD/Gv6/wrcYXy5koz4y8dRqXZtGvoc0VWUDzWnBYMQEBG2nmOYC5G6McQ9BmDx4OF87w1 vnxRNlqLwuHgl9jkDfCCuwOe99j4HoazKUy46yw4w5zbHDiLrTiRWzlxqmDAKBPNpBC3WT XLBBTN4PVOzTnm4pvMmbTyTZOa3kY6kt5hU+6zicfLmRuiMJrLthYfYgMrumAg== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1761659878; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: in-reply-to:in-reply-to:references:references; bh=q4sSQfkLnUOR6EYFSrWyzoEwtf3zqvnnuhYr4uBXt5w=; b=ZyyuACtX6WpVEwXwNANDHp34V24b0xcRAwXy5gpP9ecmQBqdeOCJKHHu1j6YtOcJWLigfB Jd3qSDCN9nglHQAg== From: Sebastian Andrzej Siewior To: Lukas Wunner Cc: Thomas Gleixner , Crystal Wood , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Clark Williams , Steven Rostedt , Dietmar Eggemann , Ben Segall , Mel Gorman , Valentin Schneider , linux-kernel@vger.kernel.org, Attila Fazekas , linux-pci@vger.kernel.org, linux-rt-devel@lists.linux.dev, Bjorn Helgaas , Mahesh J Salgaonkar , Oliver OHalloran Subject: Re: [PATCH v2] genirq/manage: Reduce priority of forced secondary interrupt handler Message-ID: <20251028135756.31PG0uHY@linutronix.de> References: <20251028120652.AJUTgtwZ@linutronix.de> Precedence: bulk X-Mailing-List: linux-pci@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: On 2025-10-28 14:44:38 [+0100], Lukas Wunner wrote: > On Tue, Oct 28, 2025 at 01:06:52PM +0100, Sebastian Andrzej Siewior wrote: > > On 2025-10-27 13:59:31 [+0100], Lukas Wunner wrote: > > > The issue does not show on non-PREEMPT_RT because the primary handler > > > runs in hardirq context and thus can preempt the threaded secondary > > > handler, clear the Root Error Status register and prevent the secondary > > > handler from getting stuck. > > > > Not sure if I mentioned it before but this is due to forced threaded > > IRQs which can also be enabled on non-PREEMPT_RT systems via `threadirqs`. > > According to the commit which introduced the "threadirqs" command line > option, 8d32a307e4fa ("genirq: Provide forced interrupt threading"), > it is "mostly a debug option". I guess the option allows testing > the waters on arches which do not yet "select ARCH_SUPPORTS_RT" > to see if force-threaded interrupts break anything. I recall the > option being available in mainline for much longer than PREEMPT_RT > and it was definitely useful as a justification to upstream changes > which were otherwise only needed by the out-of-tree PREEMPT_RT patches. There are people using it without PREEMPT_RT due to $reasons. It is not documented in Documentation/admin-guide/kernel-parameters.txt as an option meant only for debugging. > Intuitively I would assume that debug options are not worth calling out > in commit messages or code comments as users and developers will > primarily be interested in the real deal (i.e. PREEMPT_RT) and not > an option which gets us only halfway there. However if you > (or anyone else) feels strongly about it, I'll be happy to respin. I argued and sent patches to fix code which was wrong on PREEMPT_RT due to threadirqs and was also wrong without PREEMPT_RT enabled but solely with forced-threaded irqs. But please wait once tglx/irq or peterz/sched says something here before repining. > Thanks for taking a look! > > Lukas Sebastian