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 907A93F5BD1 for ; Fri, 15 May 2026 22:27:13 +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=1778884033; cv=none; b=BheiwJFpzGTDgmI7ipK1biOQpjt7Up+FYnWPqbylgeGA90Sb/JQ1W9s3BT0giHKIcIh6XI4qqji51SxxC+MEP7MX9gMMFV45zdaczn+L/5fqD2Ise+yttYf425znWjnLWp1E0/fBm43YUSuoGm5LaPnIw0KFzA9zbMYw1D/73Zw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778884033; c=relaxed/simple; bh=otosoVi+JIdd9UtemTmMFwkI9cY7WTsWHpy0jTvaD2A=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=tE/eGjeYmHL+ukOJI+4pdpCyvOAn1M2XL+IVPIgdZiyLWahpy6hSCde/5Qtjkkr9IVK+e0IiWML5kywG6R2QmxsryHCMdOtbhFpNFPmMTE6krYJ5aSsCZPfCHDWnNYrca1Udm6TaNCkrsNI+9TOi4KeU1IskXWD1qFY67zVtEXg= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=WCEkCSqh; 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="WCEkCSqh" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 07C50C2BCB0; Fri, 15 May 2026 22:27:12 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778884033; bh=otosoVi+JIdd9UtemTmMFwkI9cY7WTsWHpy0jTvaD2A=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=WCEkCSqhu5RGpHElkyulCcwwI96Jv/srcba9jyb46JQl16+h2ebJRfyktC24yqKu2 N0pe1tIwT5pqx+mkHsfmHKLExOZfx3i7nm8+sROIw0fsu5tg12guItvdNslAjGMZsJ VPP5biUdvuSxYW3zQ0QAStDRN7uCEhxN08qH7VSV1tJfeNCUnz74NeltJXom1nkNx7 J4zjg8VWsPQM8StkkZREjV37nex2FZA0nnLvdOANumW1sCzkqMT8igPV37FR/dcZjU y3/WlrSbfVOw6OSfHuiswfcwsyjiJ4gEMeWd+F/MDpqIFmB37VS9PD90hgPTAiS+U/ NtFuoE3vNJTvw== Date: Fri, 15 May 2026 12:27:12 -1000 From: Tejun Heo To: Steven Rostedt Cc: LKML , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , Kyle McMartin Subject: Re: [PATCH v2] sched/rt: Have RT_PUSH_IPI be default off for non PREEMPT_RT Message-ID: References: <20260515103740.25ccbed8@gandalf.local.home> <20260515143847.543c4b8c@gandalf.local.home> <20260515145608.2039b4cf@gandalf.local.home> Precedence: bulk X-Mailing-List: linux-kernel@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: <20260515145608.2039b4cf@gandalf.local.home> Hello, On Fri, May 15, 2026 at 02:56:08PM -0400, Steven Rostedt wrote: > I just want to make sure that my analysis is correct. Since only one CPU > can initiate the RT_PUSH_IPI. That for this to be a problem, other CPUs > need to be constantly running RT tasks for short periods of time so that > when the RT task schedules off the CPU, the CPU then initiates the "pull". > And it's not that it happens all at once. It's more serialized where the RT > tasks are scheduling off at different times to constantly feed the > RT_PUSH_IPI logic without seeing that it's already in place. > > It would require this to happen enough times to keep the overloaded CPU > from finishing the softirq until a time when the softirq is scheduled > again. And it would maintain this abuse for long enough to trigger the > watchdog. > > Does that fit the scenario of your environment? Yeah, I think that's coming from the FIFO threaded irq handling for mpi3mr. We tried two mitigations - one dropping the irq threads to SCHED_OTHER and NO_RT_PUSH_IPI. Both worked. While the former is not conclusive in itself, it is in line with the theory at least. Thanks. -- tejun