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([2001:b07:6468:f312:5e2c:eb9a:a8b6:fd3e]) by smtp.gmail.com with ESMTPSA id eg31sm770602edb.38.2021.10.06.06.36.25 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 06 Oct 2021 06:36:26 -0700 (PDT) Message-ID: Date: Wed, 6 Oct 2021 15:36:24 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.1.0 Subject: Re: [PATCH MANUALSEL 5.14 3/9] KVM: do not shrink halt_poll_ns below grow_start Content-Language: en-US To: Sasha Levin , linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Sergey Senozhatsky , kvm@vger.kernel.org References: <20211006133021.271905-1-sashal@kernel.org> <20211006133021.271905-3-sashal@kernel.org> From: Paolo Bonzini In-Reply-To: <20211006133021.271905-3-sashal@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On 06/10/21 15:30, Sasha Levin wrote: > From: Sergey Senozhatsky > > [ Upstream commit ae232ea460888dc5a8b37e840c553b02521fbf18 ] > > grow_halt_poll_ns() ignores values between 0 and > halt_poll_ns_grow_start (10000 by default). However, > when we shrink halt_poll_ns we may fall way below > halt_poll_ns_grow_start and endup with halt_poll_ns > values that don't make a lot of sense: like 1 or 9, > or 19. > > VCPU1 trace (halt_poll_ns_shrink equals 2): > > VCPU1 grow 10000 > VCPU1 shrink 5000 > VCPU1 shrink 2500 > VCPU1 shrink 1250 > VCPU1 shrink 625 > VCPU1 shrink 312 > VCPU1 shrink 156 > VCPU1 shrink 78 > VCPU1 shrink 39 > VCPU1 shrink 19 > VCPU1 shrink 9 > VCPU1 shrink 4 > > Mirror what grow_halt_poll_ns() does and set halt_poll_ns > to 0 as soon as new shrink-ed halt_poll_ns value falls > below halt_poll_ns_grow_start. > > Signed-off-by: Sergey Senozhatsky > Signed-off-by: Paolo Bonzini > Message-Id: <20210902031100.252080-1-senozhatsky@chromium.org> > Signed-off-by: Paolo Bonzini > Signed-off-by: Sasha Levin > --- > virt/kvm/kvm_main.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index b50dbe269f4b..1a11dcb670a3 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -3053,15 +3053,19 @@ static void grow_halt_poll_ns(struct kvm_vcpu *vcpu) > > static void shrink_halt_poll_ns(struct kvm_vcpu *vcpu) > { > - unsigned int old, val, shrink; > + unsigned int old, val, shrink, grow_start; > > old = val = vcpu->halt_poll_ns; > shrink = READ_ONCE(halt_poll_ns_shrink); > + grow_start = READ_ONCE(halt_poll_ns_grow_start); > if (shrink == 0) > val = 0; > else > val /= shrink; > > + if (val < grow_start) > + val = 0; > + > vcpu->halt_poll_ns = val; > trace_kvm_halt_poll_ns_shrink(vcpu->vcpu_id, val, old); > } > Acked-by: Paolo Bonzini