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[23.128.96.18]) by mx.google.com with ESMTP id b1si1222046ejb.418.2021.05.15.03.38.01; Sat, 15 May 2021 03:38:24 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18; Authentication-Results: mx.google.com; dkim=pass header.i=@google.com header.s=20161025 header.b=Ma9YTpFK; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=REJECT sp=REJECT dis=NONE) header.from=google.com Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232807AbhENVeX (ORCPT + 99 others); Fri, 14 May 2021 17:34:23 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34598 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232548AbhENVeW (ORCPT ); Fri, 14 May 2021 17:34:22 -0400 Received: from mail-lf1-x129.google.com (mail-lf1-x129.google.com [IPv6:2a00:1450:4864:20::129]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 98E47C061756 for ; Fri, 14 May 2021 14:33:10 -0700 (PDT) Received: by mail-lf1-x129.google.com with SMTP id z9so320583lfu.8 for ; Fri, 14 May 2021 14:33:10 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20161025; h=mime-version:references:in-reply-to:from:date:message-id:subject:to :cc; bh=DgAKwIM9zch8xYFNPJtzcIGRCfmQye33dMFzHuDOjA8=; b=Ma9YTpFKv2FKqspm+/+nOYKxqwaYNdETxuDqxtZyA7ZnVB17mpdfo0ZQZ1QAMyP7bQ 2NoTwneXD9c+6ebVHoiqc6oePXLumrECPiQv+8vOzySGekm4yv4qyr/1A5OQgNBWIdOc GC91s86KWPnv8OcKzcAtpmA6LtDhi2dV4QHzddOOZPk3XWb4BwhtopFJddjuMGi0t41q Jt0ib/JJrlJ/eTK/VFDyP2XjLu/w++ESDctvgTGDtx+T4x5lrWiNYYxvwr1aWxUfB5gb DYjv0/UJb4ygI1UCeFfyaQGMxfketFlRyTTSsDTQ0S3dPSWKpNzYhoYbxy3ooFhgS+3n 2mNg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:mime-version:references:in-reply-to:from:date :message-id:subject:to:cc; bh=DgAKwIM9zch8xYFNPJtzcIGRCfmQye33dMFzHuDOjA8=; b=cL0diZN3jkWu1SF1Gq+YEi6zTFLwWhkaYOLCCy784FmfYoK0+kyyF/l1jvdLnnHEms w7tEbHILSC8iRrkmTeKM1+UO0SCmfp7//zQK0BHPxHKKqevBLDadVCwjtcopujKTEvPS 0MvrV9utJnzwW2p003khBEFu+YacQDzelzKrNxHUcCAXtEmInMRpWNOj2HssgM/cNezp s1kCeZLlIaclz2R+DdX38tC1uIo/EOtskLkB2Q6shNVsOAe+YwjwTd0BGa/2RPo4Agez 5AfakYoMDboVsNR2RkWPQzzheNgBGOWfO0a5I32+sMJbLN4qeQuJq6SiUIoOBLqvIIE8 NsHA== X-Gm-Message-State: AOAM531I2G208w4R6B8ychfkon+lLe5YT01mzpuZQPHfHuOLvh17JLM+ xnhKRuxa2fBgKJHZE8TEgl0VsGY+y8ZZeBI1JjNQJQ== X-Received: by 2002:a05:6512:2243:: with SMTP id i3mr33685984lfu.46.1621027988910; Fri, 14 May 2021 14:33:08 -0700 (PDT) MIME-Version: 1.0 References: <1620871189-4763-1-git-send-email-wanpengli@tencent.com> In-Reply-To: <1620871189-4763-1-git-send-email-wanpengli@tencent.com> From: David Matlack Date: Fri, 14 May 2021 14:32:42 -0700 Message-ID: Subject: Re: [PATCH v2 2/4] KVM: X86: Bail out of direct yield in case of under-comitted scenarios To: Wanpeng Li Cc: linux-kernel@vger.kernel.org, kvm list , Paolo Bonzini , Sean Christopherson , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel Content-Type: text/plain; charset="UTF-8" Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, May 12, 2021 at 7:01 PM Wanpeng Li wrote: > > From: Wanpeng Li > > In case of under-comitted scenarios, vCPU can get scheduling easily, > kvm_vcpu_yield_to adds extra overhead, we can observe a lot of race > between vcpu->ready is true and yield fails due to p->state is > TASK_RUNNING. Let's bail out in such scenarios by checking the length > of current cpu runqueue, it can be treated as a hint of under-committed > instead of guarantee of accuracy. > > Signed-off-by: Wanpeng Li > --- > v1 -> v2: > * move the check after attempted counting > * update patch description > > arch/x86/kvm/x86.c | 3 +++ > 1 file changed, 3 insertions(+) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 9b6bca6..dfb7c32 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -8360,6 +8360,9 @@ static void kvm_sched_yield(struct kvm_vcpu *vcpu, unsigned long dest_id) > > vcpu->stat.directed_yield_attempted++; > > + if (single_task_running()) > + goto no_yield; Since this is a heuristic, do you have any experimental or real world results that show the benefit? > + > rcu_read_lock(); > map = rcu_dereference(vcpu->kvm->arch.apic_map); > > -- > 2.7.4 >