From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 1CDF631E852; Thu, 14 May 2026 21:15:33 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778793333; cv=none; b=T96rkNo4ou3lTYMODRF9jkkXs2K9Y+njZeSDfqF0qB1jfT6Zj9aWQu1baPUfuF4t4LNKK74480I+0KjbH4w8TIeekcx2NfwON7UbiJHSG4C7UhwaA8JxWZAajuiAe6w95O1fnfmswg17z6rEcD09VmQiZiiF5yJ7cCWPf/KzVSs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778793333; c=relaxed/simple; bh=zn5jP5uribMvXcgpJ0rp7zvAd2mUNvr/nvoMbhIOkfc=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=QWX1rWB2NsYr5uWcSJ8XOW5AKMe8vzWx6bBPNwWscHZb3JHSCYpa5Hmf/tAIgUfiYvThLgQwG1aFlutqxeN3gO6qMDnSqwAq9L3UUMOnbZU1QnjdHND4VACXoXscdfLHpZKGSPWp1rpjPxqS5O3s7GOtW+paZjDv97Qfky9vc7o= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=or8IOM16; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="or8IOM16" Received: by smtp.kernel.org (Postfix) with ESMTPSA id CC5B3C2BCB3; Thu, 14 May 2026 21:15:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778793332; bh=zn5jP5uribMvXcgpJ0rp7zvAd2mUNvr/nvoMbhIOkfc=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=or8IOM16rev9cFQwpI4jVqNDZ0q7GVW/e0EcNWlKzYjXyFvzub2zbIGW0G86qE1Ue +ApV+i2W9qfuPfuDnJN7qTwGz4SGodhJnuNUR6R8CqNd2igNcTBFCQg1EIqIjYxPEW DLAUnzrQuogcEl+oYZfSE1aGPttEr4bE7dDe+IxFTTslZqT8AcD3RZw1wIK5nCJNtw /TCIXQ+tr1cmGoNMelfW/bcJFQ33GXrC/S+lAhUNW0zKmNg+Lb4cSg6fh4/u9+3jwa FmloQsEmx5m+Amv6sFhdn3wM8bMcdOL967THrwGmBYsGI+uxd2kXUiN723V//eJ5u0 BMo0ZQ0HyBtpA== Date: Thu, 14 May 2026 11:15:31 -1000 From: Tejun Heo To: Steven Rostedt Cc: Peter Zijlstra , Ingo Molnar , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , Kyle McMartin , linux-kernel@vger.kernel.org, stable@vger.kernel.org, Linux RT Development , Clark Williams , Sebastian Andrzej Siewior , John Kacur Subject: Re: [PATCH sched/core] sched/rt: Fix RT_PUSH_IPI soft lockup loop Message-ID: References: <056f95bc5805f7e161458984fff4b3cb@kernel.org> <20260512172847.5024e5e8@gandalf.local.home> <20260513193914.1593369-1-tj@kernel.org> <20260513202432.18dd7b9f@gandalf.local.home> <20260513213108.2870a1e7@fedora> <20260513220136.5a11c740@fedora> <20260514100300.1d594c7a@gandalf.local.home> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20260514100300.1d594c7a@gandalf.local.home> Hello, Steven. On Thu, May 14, 2026 at 10:03:00AM -0400, Steven Rostedt wrote: > I was thinking about this more and does disabling the RT_PUSH_IPI cause any > problems for you? > > # echo NO_RT_PUSH_IPI > /sys/kernel/debug/sched/features Not at all. This is actually the mitigation that we deployed across the affected machines. ... > -/* RT IPI pull logic requires IRQ_WORK */ > -#if defined(CONFIG_IRQ_WORK) && defined(CONFIG_SMP) > +/* > + * RT IPI pull logic requires IRQ_WORK and doesn't make sense for uniprocessors. > + * If CONFIG_IRQ_FORCED_THREADING isn't set, then softirqs do not run as threads > + * and can cause latency larger than what RT_PUSH_IPI can save, killing the > + * effect of it. > + */ > +#if defined(CONFIG_IRQ_WORK) && defined(CONFIG_SMP) && \ > + defined(CONFIG_IRQ_FORCED_THREADING) > # define HAVE_RT_PUSH_IPI > #endif Maybe it should trigger on force_irqthreads so that it's active only when irq threads are actully enabled. Whichever way it's done tho, wouldn't this still leave machines in that config susceptible to IPI storms? It took a combination of factors to trigger - mpi3mr's threaded irq, psimon activated by systemd, and sustained network load - but those factors are not that exotic. Thanks. -- tejun