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Thu, 29 Oct 2026 16:36:29 +0000 (GMT) Received: from [9.87.137.195] (unknown [9.87.137.195]) by smtpav03.fra02v.mail.ibm.com (Postfix) with ESMTP; Thu, 29 Oct 2026 16:36:29 +0000 (GMT) Message-ID: Date: Thu, 29 Oct 2026 17:36:28 +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 v14 04/13] cpumask: Introduce cpu_preferred_mask To: Yury Norov Cc: Shrikanth Hegde , linux-kernel@vger.kernel.org, mingo@kernel.org, peterz@infradead.org, juri.lelli@redhat.com, vincent.guittot@linaro.org, yury.norov@gmail.com, kprateek.nayak@amd.com, iii@linux.ibm.com, corbet@lwn.net, tglx@kernel.org, gregkh@linuxfoundation.org, pbonzini@redhat.com, seanjc@google.com, vschneid@redhat.com, huschle@linux.ibm.com, rostedt@goodmis.org, dietmar.eggemann@arm.com, maddy@linux.ibm.com, srikar@linux.ibm.com, hdanton@sina.com, chleroy@kernel.org, vineeth@bitbyteword.org, frederic@kernel.org, arighi@nvidia.com, pauld@redhat.com, christian.loehle@arm.com, tj@kernel.org, tommaso.cucinotta@gmail.com, maz@kernel.org, rafael@kernel.org, rdunlap@infradead.org, kernellwp@gmail.com, linux-doc@vger.kernel.org, jgross@suse.com, virtualization@lists.linux.dev, sunlightlinux@gmail.com References: <20260928053728.797539-1-sshegde@linux.ibm.com> <20260928053728.797539-5-sshegde@linux.ibm.com> <4605dad5-aab2-49e3-b919-bf9897181834@linux.ibm.com> Content-Language: en-US From: Mete Durlu In-Reply-To: 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-Proofpoint-ORIG-GUID: 9lqEBvvs7gzC6DkqD5lU8d1OxFLpQkgh X-Proofpoint-Spam-Details-Enc: AW1haW4tMjYxMDI5MDA2MyBTYWx0ZWRfX6WBcxdgMKUDo h37iJT9VaH2+Fmruih3d4KNT0Zga7F3Gibbjuh0KNOmbApUASxzZtRvpEpTlpgg+eyIz2i6hfEb XghuijwKrgEm2i4mYxCZZWZpA3l4aW/5indrmbiHu7bK1EQtbBNbl0rQXU9BmTZT65O1Vt48LXa Z5O0sqvTZnfQXdETjBBW+cn0FTr0I1863s+Kgky6OReCDmCkSNQunhhngLEDh+GiAnbUOsXdtB3 pnwpoDCDu0ehYRZFK1eqsBw6eYapRfBdJAJtG5wfP31DRwloUIFnw+DLAlRXl2xTuPKflSvRSeZ fGiYUuNbLk/9+pxLDAmv2fHKjIbcANeX5RgRuSgfeXjzclxpVPuEsVpK1ni0gK3d4+KikV3BSl/ 9BcKG7SwDFL4o3Ndh70ey3WVua/rhw== X-Authority-Analysis: v=2.4 cv=BOMmP1QG c=1 sm=1 tr=0 ts=6ae37617 cx=c_pps a=AfN7/Ok6k8XGzOShvHwTGQ==:117 a=AfN7/Ok6k8XGzOShvHwTGQ==:17 a=IkcTkHD0fZMA:10 a=660iZSQnnn4A:10 a=VkNPw1HP01LnGYTKEx00:22 a=RnoormkPH1_aCDwRdu11:22 a=V8glGbnc2Ofi9Qvn3v5h:22 a=NEAV23lmAAAA:8 a=VnNF1IyMAAAA:8 a=PUpFx_WVMNND69PTjbIA:9 a=3ZKOabzyN94A:10 a=QEXdDO2ut3YA:10 X-Proofpoint-GUID: uH0D07jxJuGJFGnKTapMZ_5XyfkvOLip X-Proofpoint-Spam-Info: AW1haW4tMjYxMDI5MDA2MyBTYWx0ZWRfX6XDD5fdTB6UU cs7G/bBoZ1HXKQ0mH4vrVLQZ5GfhU6ZjpKzHByV1hGfwOTgPNBjX4/rAzvVk5p4xN6MpEvRb3p9 PgekaDfWJI62/C+qhhptARwaIiMhZbM= 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=2026-10-29_05,2026-10-21_02,2025-10-01_01 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 suspectscore=0 bulkscore=0 malwarescore=0 adultscore=0 phishscore=0 spamscore=0 lowpriorityscore=0 classifier=typeunknown authscore=0 authtc= authcc= route=outbound adjust=0 reason=mlx scancount=1 engine=8.22.0-2610190000 definitions=main-2610290063 On 29/10/2026 17:28, Yury Norov wrote: > On Thu, Oct 29, 2026 at 02:32:08PM +0100, Mete Durlu wrote: >> On 28/09/2026 07:37, Shrikanth Hegde wrote: >>> Provide the preferred CPU infrastructure. Define get/set macros >>> which could be used to get/set CPU state as preferred. >>> >>> CONFIG_PREFERRED_CPU will be selected by the driver which handles >>> steal time values. It is going to set/clear preferred CPU state. >>> This driver will be called steal_governor and it is introduced in >>> subsequent patches. It periodically computes the steal ratio and >>> decides on preferred CPU state. >>> >>> A CPU is set to preferred when it becomes active. Later it may be >>> marked as non-preferred depending on steal ratio by the steal_governor. >>> >>> Always maintain design construct of preferred is subset of active. >>> i.e. preferred ⊆ active ⊆ online ⊆ present ⊆ possible >>> >>> With CONFIG_PREFERRED_CPU=n, ensure set_cpu_preferred is a nop and get >>> method returns the active state in that case. >>> >>> Signed-off-by: Shrikanth Hegde >>> --- >>> include/linux/cpumask.h | 24 ++++++++++++++++++++++++ >>> kernel/Kconfig.preempt | 4 ++++ >>> kernel/cpu.c | 6 ++++++ >>> kernel/sched/core.c | 5 +++++ >>> 4 files changed, 39 insertions(+) >> >> [..snip..] >> >>> #define cpu_is_offline(cpu) unlikely(!cpu_online(cpu)) >>> diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt >>> index 985aea617cfe..edc067a0c422 100644 >>> --- a/kernel/Kconfig.preempt >>> +++ b/kernel/Kconfig.preempt >>> @@ -194,3 +194,7 @@ config SCHED_CLASS_EXT >>> For more information: >>> Documentation/scheduler/sched-ext.rst >>> https://github.com/sched-ext/scx >>> + >>> +config PREFERRED_CPU >>> + bool >>> + depends on SMP && PARAVIRT >> FWICT, PREFERRED_CPU mechanism can work perfectly fine without PARAVIRT >> selected. It would be annoying to enable it and implement a dummy >> paravirt_steal_clock() just for that. >> >> Shrikanth, would it be possible to drop that dependency? > > Do you have a non-paravirt case in mind? s390 LPARs are exactly that. s390 does not select PARAVIRT by default but enabling PREFERRED_CPU is strongly considered. I removed the PARAVIRT dependency and gave the whole thing a quick spin. Builds and functions w/o any issues on s390! > I'm actually about to submit an RFC that drops the PARAVIRT dependency > and provides write access to the preferred mask. But I want to make > sure that we need it, and we've got no reasonable mechanism to put > unneeded CPUs on idle already. You can mention s390 LPARs as valid case on your RFC if need be. Thank you!