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Mon, 2 Nov 2026 10:16:30 +0000 (GMT) Received: from [0.0.0.0] (unknown [9.111.80.131]) by smtpav03.fra02v.mail.ibm.com (Postfix) with ESMTP; Mon, 2 Nov 2026 10:16:30 +0000 (GMT) Message-ID: <388636ac-4521-4523-bb5b-b6bc71591ff6@linux.ibm.com> Date: Mon, 2 Nov 2026 11:16:30 +0100 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 1/6] sched: decouple PREFERRED_CPU from PARAVIRT in Kconfig.preempt To: Yury Norov , Peter Zijlstra , Ingo Molnar , Thomas Gleixner , Juri Lelli , Vincent Guittot , Shrikanth Hegde Cc: Yury Norov , "Rafael J. Wysocki" , Alexander Gordeev , Andrea Righi , Ben Segall , Christian Borntraeger , Danilo Krummrich , Dietmar Eggemann , Greg Kroah-Hartman , Heiko Carstens , Johan Hovold , Jonathan Corbet , K Prateek Nayak , Mel Gorman , Mete Durlu , Randy Dunlap , Rasmus Villemoes , Shuah Khan , Steven Rostedt , Sven Schnelle , Valentin Schneider , Vasily Gorbik , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, driver-core@lists.linux.dev, linux-s390@vger.kernel.org References: <20261101192203.6979-1-ynorov@nvidia.com> <20261101192203.6979-2-ynorov@nvidia.com> Content-Language: en-US From: Ilya Leoshkevich In-Reply-To: <20261101192203.6979-2-ynorov@nvidia.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 X-Proofpoint-Reinject: loops=2 maxloops=12 X-Proofpoint-GUID: KIKmBXBbZxQ0AgfSqcziIZ-8sh-ULZ7d X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMTAyMDA0MCBTYWx0ZWRfX4b8mYsBsQI90 Cds463mvoN7ipqKAPcMhRG9cv2cmJH7imu+pBNAKUzYHZ0l4QRzT6OtWfocplphprbRPPcKUhK/ ewKqcPIRH7GGJrL7xKQ6XpJdqzz6TgjaSI2ivY9JJSH24KlUEbBGsMe1i/6f5ENqM879+1V5uPD sHhZ4aVMl3Pdx2HGeXnZi+d6SkpJ3e8JhVA1w8B3k3EXRQ2QR0Jqk7PjHrb+DTMkBbYibeR51hS VrEvAoc0qhDJfiKUG9iErQN23vYv4ulZFh2ZkIAD9qD868BkZG/JdGutezE7uDx0M6feE3lY0/p Q2/IrS40JQRVOvH/Tbt71zjIvhJ3L1/wcVe/5WSEHuFXw3yIITyGLzWEciPGhWv2r/PFqggQO8V KN7P2Zs3c+rVLq4CD8Uif+/PadLgHrZW2Z3Tv4UTrGYCQKnjwQ1MUZYQwaukbcXEphkvBg4eSxc fMN9UME+CtgYLDm7V1g== X-Proofpoint-Spam-Info: AW1haW4tMjYxMTAyMDA0MCBTYWx0ZWRfX+121CA8UooYf y/fpWTXMJ/RyZzfqKMtOEDj2zgmYMzNR35/LU/M2zk1es7XQ8dDO6azVrWHx5Jiyb/KXWV8XJxR TWAIxg88JFalGqTloUcrvtjAqcF7tLw= X-Authority-Analysis: v=2.4 cv=QK391QLL c=1 sm=1 tr=0 ts=6ae86305 cx=c_pps a=5BHTudwdYE3Te8bg5FgnPg==:117 a=5BHTudwdYE3Te8bg5FgnPg==:17 a=IkcTkHD0fZMA:10 a=zJRp6_cAMcgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=Ikd4Dj_1AAAA:8 a=Oo2n8jX_zgt0tV1EdkUA:9 a=QEXdDO2ut3YA:10 X-Proofpoint-ORIG-GUID: BeEFtssz9nEvVgG4jeq4H4_xQzJd-ycM X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.293,Aquarius:18.0.1176,Hydra:6.1.138,FMLib:17.12.100.49 definitions=2026-11-02_03,2026-10-21_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 spamscore=0 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 impostorscore=0 clxscore=1011 lowpriorityscore=0 adultscore=0 priorityscore=1501 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2610300000 definitions=main-2611020040 On 11/1/26 20:21, Yury Norov wrote: > The IBM s390 doesn't enable PARAVIRT config for their hardware > virtualized Logical Partitions (LPAR). However, the steal time is > accounted for the LPARs, once the config VIRT_CPU_ACCOUNTING_NATIVE > is enabled. > > Preferred cpumask doesn't rely on any feature gated by PARAVIRT config, > and requires it to minimize the configuration space and runtime overhead, > with the lack of non-paravirt user. Now that s390 wants to adopt preferred > cpumask, there's no reason to keep it coupled to paravirt. > > Make PREFERRED_CPU a user-configurable option, even if paravirtualization > is not enabled, and drop PARAVIRT dependency on the steal governor. > > Keep the default module selection conditional on PARAVIRT so other SMP > configurations can opt in without enabling the governor by default. > > Link: https://lore.kernel.org/all/4605dad5-aab2-49e3-b919-bf9897181834@linux.ibm.com/ > CC: Mete Durlu > Signed-off-by: Yury Norov > --- > Can be applied independently from the rest of the series. > > drivers/virt/Kconfig | 8 ++++++-- > kernel/Kconfig.preempt | 12 ++++++++++-- > 2 files changed, 16 insertions(+), 4 deletions(-) This is really useful to us, since even though s390 is nominally paravirtualized, it does not technically benefit from defining CONFIG_PARAVIRT. Specifically, steal time accounting happens by computing a difference between wall time and CPU time, and not by explicitly querying the hypervisor. Thanks! Reviewed-by: Ilya Leoshkevich [...]