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[91.219.240.2]) by smtp.gmail.com with ESMTPSA id z13sm3715665wrs.71.2021.08.26.09.17.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 26 Aug 2021 09:17:52 -0700 (PDT) From: Vitaly Kuznetsov To: Sean Christopherson Cc: kvm@vger.kernel.org, Paolo Bonzini , Wanpeng Li , Jim Mattson , "Dr. David Alan Gilbert" , Nitesh Narayan Lal , Lai Jiangshan , linux-kernel@vger.kernel.org Subject: Re: [PATCH v3 3/4] KVM: Optimize kvm_make_vcpus_request_mask() a bit In-Reply-To: References: <20210826122442.966977-1-vkuznets@redhat.com> <20210826122442.966977-4-vkuznets@redhat.com> Date: Thu, 26 Aug 2021 18:17:51 +0200 Message-ID: <87fsuwi3io.fsf@vitty.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org Sean Christopherson writes: > On Thu, Aug 26, 2021, Vitaly Kuznetsov wrote: >> Iterating over set bits in 'vcpu_bitmap' should be faster than going >> through all vCPUs, especially when just a few bits are set. >> >> Signed-off-by: Vitaly Kuznetsov >> --- > > ... > >> + if (vcpu_bitmap) { >> + for_each_set_bit(i, vcpu_bitmap, KVM_MAX_VCPUS) { >> + vcpu = kvm_get_vcpu(kvm, i); >> + if (!vcpu || vcpu == except) >> + continue; >> + kvm_make_vcpu_request(kvm, vcpu, req, tmp, me); >> + } >> + } else { >> + kvm_for_each_vcpu(i, vcpu, kvm) { >> + if (vcpu == except) >> + continue; >> + kvm_make_vcpu_request(kvm, vcpu, req, tmp, me); >> } >> } > > Rather than feed kvm_make_all_cpus_request_except() into kvm_make_vcpus_request_mask(), > I think it would be better to move the kvm_for_each_vcpu() path into > kvm_make_all_cpus_request_except() (see bottom of the mail). That eliminates the > silliness of calling a "mask" function without a mask, and also allows a follow-up > patch to drop @except from kvm_make_vcpus_request_mask(), which is truly nonsensical > as the caller can and should simply not set that vCPU in the mask. Both make perfect sense, thanks! v4 is being prepared. -- Vitaly