From mboxrd@z Thu Jan 1 00:00:00 1970 Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.remote-ip=148.163.158.5 ARC-Seal: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; cv=none; t=1793626937; b=0gKA5ZWFldDZ+g4J0jRw84+Y/uMZ97J6PqEmrXfLDkCd9nUTkFslriCZn9albCFWH6GT 2slFg8xUAygnJ+56MHscjIkdtmyB2xO3SDCXpMRVI2kdBw9wF/4n0zQ67Qsdi+kWiJZaQ irdg/haOhSavHbmk9S4f/uQ3sCtgfSYqy5FS8Xxk0IxgTmuhC9f2J16mTjps1s5JcQKt1 py3Z0aw9CsdV+wz09CxjDrtUGdKDj0MB3kEIP4NMtQLodU0Qz9C8xX7z8J8yjtyqXTicC RqhzVviYVgDpzxi6uUXXrHtLYEP7WdBR3vh9xW3IgVGND/X3JyRNuH60CIwpR9GUviA== ARC-Message-Signature: i=1; d=subspace.kernel.org; s=arc20261015; a=rsa-sha256; c=relaxed/relaxed; t=1793626937; h=DMARC-Filter:Received:DKIM-Signature:Received:Received:Received: Received:Received:Received:Received:Message-ID:Date:MIME-Version: User-Agent:Subject:To:Cc:References:Content-Language:From:In-Reply-To: Content-Type:Content-Transfer-Encoding:X-TM-AS-GCONF: X-Proofpoint-Reinject:X-Authority-Analysis:X-Proofpoint-Spam-Info: X-Proofpoint-Spam-Details-Enc:X-Proofpoint-GUID: X-Proofpoint-ORIG-GUID:X-Proofpoint-Virus-Version: X-Proofpoint-Spam-Details; bh=UEpcSuoFqEU8xXewyaWkpW5bmOJntelIEVu5k49doYk=; b=ZB5hLZcIkXOXq9EpvMyXDfrDOH/CQjMBgq0PI+DpoMJsag+hXSFB2oXG7svbvXxmj57T 7J6akg8AI6Y+L2+lqCsLef++/qRzDDvpilAIOqK3tlDF4Q/oUf8/B7d6MBkacfWGGirHE uw/JI4tEOjf06KybFgg/uJ2r3kXwso8VDIeTfKJIdgAZ46Z+y6D6fk1gRihqhoDQsOOYT J38iJZo5/j2vHyBb9Z9bOHlape2avxZc81akREOzd+ACQgJ5GUHsHT/IrsLfWDD5ZPEd2 SegOvDuGFmyeGmgn4UAmAPJFwnsX7ArfVVkFG/eALJNJJEcvCG6UaEuxQ80y7dqJmxg== ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass header.from=linux.ibm.com; spf=pass smtp.mailfrom=linux.ibm.com; dkim=pass header.d=ibm.com header.i=@ibm.com header.a=rsa-sha256 header.s=pp1 header.b=WGDyMGgm; arc=none smtp.remote-ip=148.163.158.5 Received: from mx0b-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature ECDSA (prime256v1) server-digest SHA256) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E0B84606A326; Mon, 2 Nov 2026 13:42:16 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.2 smtp.subspace.kernel.org E0B84606A326 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=linux.ibm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=linux.ibm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key, unprotected) header.d=ibm.com header.i=@ibm.com header.a=rsa-sha256 header.s=pp1 header.b=WGDyMGgm Received: from pps.filterd (m0360072.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.18.1.11/8.18.1.11) with ESMTP id 6A2DEgSR2988247; Mon, 2 Nov 2026 13:41:45 GMT DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ibm.com; h=cc :content-transfer-encoding:content-type:date:from:in-reply-to :message-id:mime-version:references:subject:to; s=pp1; bh=UEpcSu oFqEU8xXewyaWkpW5bmOJntelIEVu5k49doYk=; b=WGDyMGgmcCIA+EQ+yL/0Fx CFnXpp6JQ+mK4Hm6Pjcpo+j0r9Hya4GbG1gg7J9UohE0VkWJYq5kbt0JjrNT5e1z UuYsU3TnDkOwgM/D+EQA6YhQpLBgsFPjpTH7Uqlf4dWstNCDXUeUXM085Av/9K+K nxjVk11rhS5VAsHPBSxioSkJx+jjJL0KwBwEzh0uDWRlUkuh9GA6zjaXLJ6lHy77 Mex79E6OIX8mEjeb2qUk0jCeRO0BEk4OGCZrUfPm5U2AnrIcqJlfn/lE74f4Q1xn NjhUSsYDotCWFZoZeJtkBoQChiklmYvVTwRKOYQCORt3v4XFzOBgZ9XTDNMijTEQ == Received: from ppma13.dal12v.mail.ibm.com (dd.9e.1632.ip4.static.sl-reverse.com [50.22.158.221]) by mx0a-001b2d01.pphosted.com (PPS) with ESMTPS id 4hn7yrrm6q-1 (version=TLSv1.3 cipher=TLS_AES_256_GCM_SHA384 bits=256 verify=NOT); Mon, 02 Nov 2026 13:41:44 +0000 (GMT) Received: from pps.filterd (ppma13.dal12v.mail.ibm.com [127.0.0.1]) by ppma13.dal12v.mail.ibm.com (8.18.1.11/8.18.1.11) with ESMTP id 6A2DJsRu3980386; Mon, 2 Nov 2026 13:41:43 GMT Received: from smtprelay06.fra02v.mail.ibm.com ([9.218.2.230]) by ppma13.dal12v.mail.ibm.com (PPS) with ESMTPS id 4hnvvfnug1-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Mon, 02 Nov 2026 13:41:43 +0000 (GMT) Received: from smtpav01.fra02v.mail.ibm.com (smtpav01.fra02v.mail.ibm.com [10.20.54.100]) by smtprelay06.fra02v.mail.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 6A2Dfdg747120682 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 2 Nov 2026 13:41:39 GMT Received: from smtpav01.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id A9EC720043; Mon, 2 Nov 2026 13:41:39 +0000 (GMT) Received: from smtpav01.fra02v.mail.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 665E820040; Mon, 2 Nov 2026 13:41:38 +0000 (GMT) Received: from [0.0.0.0] (unknown [9.111.80.131]) by smtpav01.fra02v.mail.ibm.com (Postfix) with ESMTP; Mon, 2 Nov 2026 13:41:38 +0000 (GMT) Message-ID: Date: Mon, 2 Nov 2026 14:41:38 +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: Shrikanth Hegde , Peter Zijlstra , Mete Durlu , Yury Norov Cc: Ingo Molnar , Thomas Gleixner , Juri Lelli , Vincent Guittot , 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 , 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> <388636ac-4521-4523-bb5b-b6bc71591ff6@linux.ibm.com> <20261102110026.GG1813469@noisy.programming.kicks-ass.net> <9273846b-d815-4c40-a7a0-960281515878@linux.ibm.com> <66ccd713-5571-4c1a-b59e-29adbc9852e3@linux.ibm.com> Content-Language: en-US From: Ilya Leoshkevich In-Reply-To: <66ccd713-5571-4c1a-b59e-29adbc9852e3@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=Mcr5KJ/f c=1 sm=1 tr=0 ts=6ae89318 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=zJRp6_cAMcgA:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=RzCfie-kr_QcCd8fBx8p:22 a=VwQbUJbxAAAA:8 a=VnNF1IyMAAAA:8 a=Ikd4Dj_1AAAA:8 a=2ZLY2jDhLclDGvpxdKIA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-Spam-Info: AW1haW4tMjYxMTAyMDA1MiBTYWx0ZWRfX69IfUWuXTaKy lgapWBy+4j0Db8jWpHuOaqVb4/k38jkUggDwHhkZ+cAL0qa1YWqK60q+fkWAeF1iHPjJdwi9Bno cnUMwqkCtBYs4YPzMDbRtGQoDYASDpk= X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMTAyMDA1MiBTYWx0ZWRfX8ehtqKALxD9L ST32w2EwWwZB9HWoyUnI+Y5+AuZNgSWl8N//MyjhJXxqXie2DwTc1GwxexF5GN6UeoomF/T9fj8 aFHCHE85Imccbx16229F9mqbt0kZnr+uriGgUaNpX8vzKCb2Yn6oABvg7yTP2c61Leh0acbPxqU Hp+lqnxFw94BYVd2LLCeotULH//5XnbuETrISaCjIN2Q1+BTxZcQLhqKnf+sxi5qf963kk7SxZ1 RkxRybBpfjXtkiz+k7opRYDIsXwI2xy0FpIl8N+AlHxQcJAJjovoYEL66PFxqtZS1usCBRs27aQ kNt3z0jmxUcbti8u0dDHSEgmXohJEwChK7TfQzcBvrwHvteajRbglWn9LgQ/0pND6l+ZKQ1Suyv yZPc4ORAkqxZHvXnDhLXr6/VCllJ1nK5Yqu0Eh68nUv5J2edaUCBhw50N8/LrjtTbnuGbfjcJBZ wMLsR1pdgyxH40C7iyg== X-Proofpoint-GUID: WV_hIbVvQLek2yXOApJDBgykXKFSyc_m X-Proofpoint-ORIG-GUID: A8u9pJY9wVFah2z3BUYt1cdxZpJkRdOT 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_03,2026-11-02_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 priorityscore=1501 clxscore=1015 impostorscore=0 adultscore=0 spamscore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2610300000 definitions=main-2611020052 On 11/2/26 14:00, Shrikanth Hegde wrote: > Hi. > > > On 11/2/26 5:04 PM, Ilya Leoshkevich wrote: >> >> >> On 11/2/26 12:00, Peter Zijlstra wrote: >>> On Mon, Nov 02, 2026 at 11:16:30AM +0100, Ilya Leoshkevich wrote: >>>> >>>> >>>> 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. >>> >>> And therefore removing PARAVIRT is the only possible solution? >>> >>>> Specifically, steal time accounting happens by >>>> computing a difference between wall time and CPU time, and not by >>>> explicitly querying the hypervisor. >>> >>> Nobody explicitly asks the hypervisor, that would be horrendously slow. >>> >>> Something trivial like this should do. >>> >>> --- >>>   arch/Kconfig                           | 9 +++++++++ >>>   arch/powerpc/platforms/pseries/Kconfig | 1 + >>>   arch/s390/Kconfig                      | 1 + >>>   drivers/virt/Kconfig                   | 2 +- >>>   4 files changed, 12 insertions(+), 1 deletion(-) >>> >>> diff --git a/arch/Kconfig b/arch/Kconfig >>> index 1163736de1f9..8980054beb52 100644 >>> --- a/arch/Kconfig >>> +++ b/arch/Kconfig >>> @@ -1080,6 +1080,15 @@ config HAVE_IRQ_TIME_ACCOUNTING >>>   config HAVE_PV_STEAL_CLOCK_GEN >>>       bool >>> +# >>> +#  Archs that can account CPUTIME_STEAL; normal route is through >>> PARAVIRT which >>> +#  selects HAVE_PV_STEAL_CLOCK_GEN. Directly selected by s390 and >>> PPC-LPAR >>> +#  which have their own thing and don't go through generic cputime >>> accounting. >>> +# >>> +config HAVE_CPUTIME_STEAL >>> +    bool >>> +    default y if HAVE_PV_STEAL_CLOCK_GEN >>> + > > Can't PARAVIRT_TIME_ACCOUNTING be the kconfig we can rely upon. > s390 can add it to the config (similar to HAVE_CPUTIME_STEAL)? > > I guess it is selected currently where the steal time reporting happens. Looking at update_rq_clock_task(), s390 would still need to provide a pointless dummy paravirt_steal_clock() implementation in this case. [...]