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Tue, 3 Mar 2026 09:15:55 +0000 (GMT) Message-ID: Date: Tue, 3 Mar 2026 09:15:55 +0000 Precedence: bulk X-Mailing-List: linux-s390@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] sched: Further restrict the preemption modes To: Douglas Freimuth , Christian Borntraeger , Ilya Leoshkevich , Peter Zijlstra , mingo@kernel.org, Thomas Gleixner , Sebastian Andrzej Siewior Cc: juri.lelli@redhat.com, vincent.guittot@linaro.org, dietmar.eggemann@arm.com, rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de, vschneid@redhat.com, clrkwllms@kernel.org, linux-kernel@vger.kernel.org, linux-rt-devel@lists.linux.dev, Linus Torvalds , linux-s390@vger.kernel.org, Matthew Rosato , Hendrik Brueckner References: <20251219101502.GB1132199@noisy.programming.kicks-ass.net> <182f110b-ac63-4db4-8b01-0e841639bc39@linux.ibm.com> <08307223-88ad-4550-963e-5d1ee315023c@linux.ibm.com> Content-Language: en-GB From: Ciunas Bennett In-Reply-To: <08307223-88ad-4550-963e-5d1ee315023c@linux.ibm.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Authority-Analysis: v=2.4 cv=M9BA6iws c=1 sm=1 tr=0 ts=69a6a6d2 cx=c_pps a=3Bg1Hr4SwmMryq2xdFQyZA==:117 a=3Bg1Hr4SwmMryq2xdFQyZA==:17 a=IkcTkHD0fZMA:10 a=Yq5XynenixoA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=U7nrCbtTmkRpXpFmAIza:22 a=rVzeq6iDyh4eWtLyzegA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: yRrZXVTmB9EbNCzREd2bXzeB1Bg7orDv X-Proofpoint-GUID: 5uJq-KMg5mrQbXFusCWoZeV0_p4HVrtt X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYwMzAzMDA2OCBTYWx0ZWRfXy+cqwaeV6Lp/ qibZkH5GwFdbbN6wmvrU4lgP77c8lhjE+hrIWFe/VqLAayvpE1nop7il4FyKgGkamPSDJzp/KSf CdPvCjNsqOLXg9eYb1KdIQ5sVQc/5ECfgQz/pcw8sAIYEsVa8j2GjDNyCGRvqvps57HXbdit4gL nrIVMZiehI/gIbcZKK7RJBObbNz/MM2IqzshAsHeiQeRf81PbMbjAAHNhgKPBXQmJkyrhKhIjAb nbSemp/0sj4CFeKuh3KQzv56HrdgXdkiBvAeXNPXYSiPj8gDGPcOlBoOjp0Kkew5JWi3SRJ2PGv gqVj37wikKqfzBKO3hJ6vZHkUKJjpMgncZENYnjPOl7bvUT36sT7u/NDsrxrcY55CCOJNf4VP06 0ocqbUpQp3qqZjDKR3Rxsgbz/G8sbrCJSiKSxsqbM3S/IXjdcN5WW1aQrYRYa9FFyVO2z9R+qSO C/RXLNDXWSdgYwxRi6g== X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1121,Hydra:6.1.51,FMLib:17.12.100.49 definitions=2026-03-02_05,2026-03-03_01,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 clxscore=1015 priorityscore=1501 spamscore=0 adultscore=0 malwarescore=0 bulkscore=0 lowpriorityscore=0 impostorscore=0 phishscore=0 suspectscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2602130000 definitions=main-2603030068 A quick update on the issue. Introducing kvm_arch_set_irq_inatomic() appears to make the problem go away on my setup. That said, this still begs the question: why does irqfd_wakeup behave differently (or poorly) in this scenario compared to the in-atomic IRQ injection path? Is there a known interaction with workqueues, contexts, or locking that would explain the divergence here? Observations: irqfd_wakeup: triggers the problematic behaviour. Forcing in-atomic IRQ injection (kvm_arch_set_irq_inatomic): issue not observed. @Peter Zijlstra — Peter, do you have thoughts on how the workqueue scheduling context here could differ enough to cause this regression? Any pointers on what to trace specifically in irqfd_wakeup and the work item path would be appreciated. Thanks, Ciunas Bennett On 25/02/2026 18:30, Douglas Freimuth wrote: > > Christian, the patch is very close to ready. The last step, I rebased on Master today to pickup the latest changes to interrupt.c. I am building that now and will test for non-SE and SE environments. I have been testing my solution for SE environments for a few weeks and it seems to cover the use cases I have tested. > >