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[35.130.123.74]) by smtp.gmail.com with ESMTPSA id 00721157ae682-7fcd2c8791csm57403137b3.26.2026.06.17.17.51.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 17 Jun 2026 17:51:04 -0700 (PDT) From: Yury Norov X-Google-Original-From: Yury Norov Date: Wed, 17 Jun 2026 20:51:02 -0400 To: Shrikanth Hegde Cc: 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, 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, mgorman@suse.de, bsegall@google.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 Subject: Re: [PATCH v4 03/20] kconfig: Provide PREFERRED_CPU option Message-ID: References: <20260617174139.155540-1-sshegde@linux.ibm.com> <20260617174139.155540-4-sshegde@linux.ibm.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=us-ascii Content-Disposition: inline In-Reply-To: <20260617174139.155540-4-sshegde@linux.ibm.com> On Wed, Jun 17, 2026 at 11:11:22PM +0530, Shrikanth Hegde wrote: > Introduce a new config named PREFERRED_CPU. > > This helps to: > - Avoid the code bloat when PREFERRED_CPU=n. In that cases preferred > is same as active. > - Avoid the ifdeffery around PREFERRED_CPU in many files. > > Since paravirtulized use case is the main driving force of this > feature, make it default for kernels with PARAVIRT=y > > Signed-off-by: Shrikanth Hegde > --- > kernel/Kconfig.preempt | 13 +++++++++++++ > 1 file changed, 13 insertions(+) > > diff --git a/kernel/Kconfig.preempt b/kernel/Kconfig.preempt > index 88c594c6d7fc..0995f5ba66eb 100644 > --- a/kernel/Kconfig.preempt > +++ b/kernel/Kconfig.preempt > @@ -192,3 +192,16 @@ config SCHED_CLASS_EXT > For more information: > Documentation/scheduler/sched-ext.rst > https://github.com/sched-ext/scx > + > +config PREFERRED_CPU > + bool "Dynamic vCPU management based on steal time" > + default y if PARAVIRT && SMP > + help > + This feature helps to reduce the steal time in paravirtualised > + environment, there by reducing vCPU preemption. Reducing vCPU > + preemption provides improved lock holder preemption and reduces > + cost of vCPU preemption in the host. If it doesn't make sense for non-paravirt kernels, then depends on PARAVIRT && SMP default y > + > + By default preferred CPUs will be same as active CPUs. Depending > + on the steal time when steal monitor is enabled, preferred CPUs > + could become subset of active CPUs. > -- > 2.47.3