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([2001:b07:6468:f312:5e2c:eb9a:a8b6:fd3e]) by smtp.googlemail.com with ESMTPSA id b13-20020a05600c4e0d00b003816cb4892csm6799721wmq.0.2022.03.01.12.17.59 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 01 Mar 2022 12:17:59 -0800 (PST) Message-ID: <815a7008-b8b0-d745-e1c3-96092e887772@redhat.com> Date: Tue, 1 Mar 2022 21:17:58 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.5.0 Subject: Re: [PATCH AUTOSEL 5.15 10/23] x86/kvm: Don't use pv tlb/ipi/sched_yield if on 1 vCPU Content-Language: en-US To: Sasha Levin , linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Wanpeng Li , tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, dave.hansen@linux.intel.com, x86@kernel.org, kvm@vger.kernel.org References: <20220301201629.18547-1-sashal@kernel.org> <20220301201629.18547-10-sashal@kernel.org> From: Paolo Bonzini In-Reply-To: <20220301201629.18547-10-sashal@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/1/22 21:16, Sasha Levin wrote: > From: Wanpeng Li > > [ Upstream commit ec756e40e271866f951d77c5e923d8deb6002b15 ] > > Inspired by commit 3553ae5690a (x86/kvm: Don't use pvqspinlock code if > only 1 vCPU), on a VM with only 1 vCPU, there is no need to enable > pv tlb/ipi/sched_yield and we can save the memory for __pv_cpu_mask. > > Signed-off-by: Wanpeng Li > Message-Id: <1645171838-2855-1-git-send-email-wanpengli@tencent.com> > Signed-off-by: Paolo Bonzini > Signed-off-by: Sasha Levin > --- > arch/x86/kernel/kvm.c | 9 ++++++--- > 1 file changed, 6 insertions(+), 3 deletions(-) > > diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c > index b656456c3a944..811c7aaf23aac 100644 > --- a/arch/x86/kernel/kvm.c > +++ b/arch/x86/kernel/kvm.c > @@ -457,19 +457,22 @@ static bool pv_tlb_flush_supported(void) > { > return (kvm_para_has_feature(KVM_FEATURE_PV_TLB_FLUSH) && > !kvm_para_has_hint(KVM_HINTS_REALTIME) && > - kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)); > + kvm_para_has_feature(KVM_FEATURE_STEAL_TIME) && > + (num_possible_cpus() != 1)); > } > > static bool pv_ipi_supported(void) > { > - return kvm_para_has_feature(KVM_FEATURE_PV_SEND_IPI); > + return (kvm_para_has_feature(KVM_FEATURE_PV_SEND_IPI) && > + (num_possible_cpus() != 1)); > } > > static bool pv_sched_yield_supported(void) > { > return (kvm_para_has_feature(KVM_FEATURE_PV_SCHED_YIELD) && > !kvm_para_has_hint(KVM_HINTS_REALTIME) && > - kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)); > + kvm_para_has_feature(KVM_FEATURE_STEAL_TIME) && > + (num_possible_cpus() != 1)); > } > > #define KVM_IPI_CLUSTER_SIZE (2 * BITS_PER_LONG) NACK Not really necessary. Paolo