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([2001:b07:6468:f312:c8dd:75d4:99ab:290a]) by smtp.gmail.com with ESMTPSA id q8sm2147629wro.32.2020.10.23.02.33.09 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 23 Oct 2020 02:33:10 -0700 (PDT) To: Peter Zijlstra , Josh Don , g@hirez.programming.kicks-ass.net Cc: Ingo Molnar , Juri Lelli , Vincent Guittot , "David S. Miller" , Jakub Kicinski , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Eric Dumazet , linux-kernel@vger.kernel.org, netdev@vger.kernel.org, kvm@vger.kernel.org, Xi Wang References: <20201023032944.399861-1-joshdon@google.com> <20201023071905.GL2611@hirez.programming.kicks-ass.net> From: Paolo Bonzini Subject: Re: [PATCH 1/3] sched: better handling for busy polling loops Message-ID: Date: Fri, 23 Oct 2020 11:33:09 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.3.1 MIME-Version: 1.0 In-Reply-To: <20201023071905.GL2611@hirez.programming.kicks-ass.net> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On 23/10/20 09:19, Peter Zijlstra wrote: >> + /* >> + * preemption needs to be kept disabled between prepare_to_busy_poll() >> + * and end_busy_poll(). >> + */ >> + BUG_ON(preemptible()); >> + if (allow_resched) >> + preempt_enable(); >> + else >> + preempt_enable_no_resched(); > NAK on @allow_resched > Since KVM is the one passing false, indeed I see no reason for the argument; you can just use preempt_enable(). There is no impact for example on the tracking of how much time was spent polling; that ktime_get() for the end of the polling period is done before calling end_busy_poll(). Paolo