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 BF8AB3AEB5C for ; Tue, 12 May 2026 14:03:33 +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=1778594613; cv=none; b=fdTDYRWKM7vjGS9V3bRFk8NglWPjx8ZDWe6keOEHkG1bG9YfHNSKiZF5fcD+vJdmc1OGF9hRjUCpTpA1ls9nouQ/kjet1C39G1cxh+zNzsBj+lJm9HOuQK1nyiMfEN21JLI33+vfJJ/ecK13Nzy88LOmImHa/XjO/77qPw1/zBU= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1778594613; c=relaxed/simple; bh=epAC3nfpxE3TPbU+kdhonxBtuD0XDUNJ2cpGkx4/GKI=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=XxR+l7hbKbEDhUDgL/ZiMcQXz130yYCxmpvPFVbsa2DwfCX9qYbbzja99NCnd7SMaN0+e7Dbk3Vq75ORzGy/sf2bULHi/R9VEZZ+A92+NDI26bWZbhVQKW7ViIWci1LDpq7Ksz1eRco3c3MB39MqVTZ0HNEjauNRguyYepOD82k= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=hYbiTHNP; 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="hYbiTHNP" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 45CC4C2BCB0; Tue, 12 May 2026 14:03:33 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1778594613; bh=epAC3nfpxE3TPbU+kdhonxBtuD0XDUNJ2cpGkx4/GKI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=hYbiTHNP3SmQL66/n3Rz3n/u9yKEHhsuyO1rxl7KFCo2JIJAE4a2ut7Ga5Ja4gIns 4b1kuZs896ZlwoAhN0FQXRt1Sv7xC6NdRmpfzP15N+scpktZiSHLFppZTwysPo8gz5 8VlP/7929TGg5noBNroKhpKbEzQ/7z+ENNUEdGrBiHksme97oSFGSUePKOMkDa6Xa/ irdPyBNPsMCiY5e5dXJS7U/vOLfG0pZnUgiVT2qmVOvTqBBJp/MvjnRk7K8AMODH8w bhGYWfSccIIlcDTQ6ury9qJfM+STWrhjaTLGqEJimv1P37s+yvALnwAwXrfBLF40xC RZ1Wsn67bh7RA== Date: Tue, 12 May 2026 16:03:31 +0200 From: Frederic Weisbecker To: Juri Lelli Cc: Ingo Molnar , Peter Zijlstra , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , K Prateek Nayak , Andrea Righi , linux-kernel@vger.kernel.org, David Haufe , Cao Ruichuang , Tejun Heo Subject: Re: [PATCH] sched/deadline: Make dl-server nohz full aware Message-ID: References: <20260512-upstream-fix-dlserver-nohzfull-b4-v1-1-a94844387ae7@redhat.com> 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=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20260512-upstream-fix-dlserver-nohzfull-b4-v1-1-a94844387ae7@redhat.com> Le Tue, May 12, 2026 at 11:02:37AM +0200, Juri Lelli a écrit : > The dl_server_timer() causes spurious IPIs on nohz_full cores, breaking > isolation guarantees. The timer executes on a housekeeping core and > eventually calls tick_nohz_dep_set_cpu(), sending IPIs to isolated cores > even when only a single task is running. > > The problem is that dl-servers are not coordinated with nohz_full tick > state. Timers can fire and send IPIs to otherwise undisturbed cores. > > Fix by managing servers in sched_can_stop_tick(): > > - When RT tasks run with CFS/SCX tasks, start the appropriate server > and keep the tick running > - When only RT tasks remain, stop all servers and allow tick to stop > (except for >1 RR tasks which need the tick for round-robin) > - When only CFS/SCX tasks remain, stop all servers before stopping tick > > Introduce dl_servers_stop_all() to reduce duplication and abstract > server management from core.c. Unify RT handling into one block that > handles both RR and FIFO cases. > > Fixes: 557a6bfc662c ("sched/fair: Add trivial fair server") > Reported-by: David Haufe > Closes: https://lore.kernel.org/lkml/CAKJHwtOw_G67edzuHVtL1xC5Vyt6StcZzihtDd0yaKudW=rwVw@mail.gmail.com > Signed-off-by: Juri Lelli I indeed observed IPIs originating from dl_server some time ago but that magically disappeared after some commit from Peter. Perhaps it came back somehow? Lemme run dynticks-testing again on latest upstream... > --- > I had to modify my first original attempt at fixing this (please take a > look at the linked report/discussion) to also take SCX into > consideration. I thought SCX was disabled when CPU isolation is running? 9f391f94a173 ("sched_ext: Disallow loading BPF scheduler if isolcpus= domain isolation is in effect") Thanks. -- Frederic Weisbecker SUSE Labs