From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-yw1-f202.google.com (mail-yw1-f202.google.com [209.85.128.202]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 1B7BF4D8C3 for ; Thu, 15 Aug 2024 17:31:46 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.202 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723743109; cv=none; b=RK8ihNPs8Um1mwnBHWpRNAZMTBljfbzRwsORGUtmUZM9FgJtOjOim9laS4bkru6uNG6jmefUF9/B9KSK9N+KkYph+bQ8L8xtaEvNEXnlO4u1T6ISNnD+PXQ1ahxGbq+ntqmu8IhO31EP44E6JDqVkTkPMsG8z7sOeswyQP/2YTQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1723743109; c=relaxed/simple; bh=QbXlSIN7Jb6zKr7Do8xhpv3pvluEnhYN3MIAUO+roak=; h=Date:In-Reply-To:Mime-Version:References:Message-ID:Subject:From: To:Cc:Content-Type; b=AFXMR1nb4O9fZbb6Yd/DiCr6TZn41P8BB4GJa/o6T+Yhl68yXNpVpgirO0UaRkHA4cZ/9iwiexPtC58KZcqG01vtwgH3WFQ73OpFf3VH/1rhr5g0AuRZ3UGtN0Bh6PGOhqJqstzTC/UmJkJXWn2mmiyJp6mo2lPjWjKft+bOD1M= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b=C9xqtquZ; arc=none smtp.client-ip=209.85.128.202 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=reject dis=none) header.from=google.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=flex--seanjc.bounces.google.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=google.com header.i=@google.com header.b="C9xqtquZ" Received: by mail-yw1-f202.google.com with SMTP id 00721157ae682-672bea19c63so19726817b3.2 for ; Thu, 15 Aug 2024 10:31:46 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20230601; t=1723743106; x=1724347906; darn=vger.kernel.org; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:from:to:cc:subject:date:message-id:reply-to; bh=37F32RQuy8+0cBTW6OKKkuSelNVTFSr/zBWZTj9nXuI=; b=C9xqtquZtAo1tz31Fxl4sP0bAZogb8j+eJAXE3bwt00wMyF56gaMDDgJfQR9P3SRhz LJQ2EBG5IP+EDMr075SN1/iLxnPK9la1WTHtY1gqrg8PdIOlYp6or6uKIEzpA29/nu1q 2vuF2oxi/wgXp2Q60j8jjx3XX1B2mbzR0JQ9pzU7kxej6snDK43DWEgSwSwS+b6i3Nhn u+gxHY2a09O6Sr9Sp8nLMDvTbVr+MvUrEbVwZGC6yu2QDjHlaOlUol9MDAfT4PxMR8SA H75Eq2Qv4SzEK4yra0Y3MK9bCcTx8rsk78ZxNNqGeo8QXOKJAD1gRfoNaCyTisgwHyP/ 59Og== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1723743106; x=1724347906; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:x-gm-message-state:from:to:cc:subject:date:message-id:reply-to; bh=37F32RQuy8+0cBTW6OKKkuSelNVTFSr/zBWZTj9nXuI=; b=PWVz9xNPuMReO39bgYsGtled1OnRb9Z2t3HCJ2BhF0427etV+KxizAoOjkWwhhiCl8 pX28hgSYL2uRDuseC2niO0SuULcPxlzTXdB/v9j0tUGmyX+h8k84Abl61qvPlToyplka p7ySVouOYNVfjyxFauAHu0C3GGwRSIGAH4FJyV4jZTPvbIaGvPz85SL7Tv8r0KxXuCF3 hlNg/vdfY25gDJMIT5/UN1jwHzhD+8HtsPckOCq2ln3rnQRVMT9wUcNsyVs6TdtPA9tv T2iuOzC5fnSC6JjiUWDFv/vCgfnKDrkZWl23kuF1Q1bQYxI8PCAGy1daYaVlU/EaGq27 UOZQ== X-Forwarded-Encrypted: i=1; AJvYcCUUy/X51s1POckRZDG6pjZZ8igm+rTMC+3CYR0LvN9IVrDoPErM5f6y+spa+Aaq7qxxQcvvgjXmzZdo0GRZwlIypqgCW06Ev2XXxQwi X-Gm-Message-State: AOJu0Yx0wyag5/hfNj0QnGpoSMHh99RLoTjx7DqUJrx2EjmG9MMfs0l5 Q0+Y2uKQANYryOCn6Yte6M42SMpN2HK+AaqfCNTHYdpem+kI/gY+ro1n4Z+tpCLetgt5zIWnpT5 chw== X-Google-Smtp-Source: AGHT+IFcExSDSrYqJfIAeCJVnOPaRKoHoSW2taeGhC9rK65ohx19AQTb8ulOz1IcFs0HZt63/1LzBvs8k7k= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a05:690c:7690:b0:69b:2f8e:4d10 with SMTP id 00721157ae682-6b1bbe2eb40mr149967b3.7.1723743106134; Thu, 15 Aug 2024 10:31:46 -0700 (PDT) Date: Thu, 15 Aug 2024 10:31:44 -0700 In-Reply-To: <20240522001817.619072-19-dwmw2@infradead.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20240522001817.619072-1-dwmw2@infradead.org> <20240522001817.619072-19-dwmw2@infradead.org> Message-ID: Subject: Re: [RFC PATCH v3 18/21] KVM: x86: Avoid gratuitous global clock reload in kvm_arch_vcpu_load() From: Sean Christopherson To: David Woodhouse Cc: kvm@vger.kernel.org, Paolo Bonzini , Jonathan Corbet , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Paul Durrant , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Daniel Bristot de Oliveira , Valentin Schneider , Shuah Khan , linux-doc@vger.kernel.org, linux-kernel@vger.kernel.org, jalliste@amazon.co.uk, sveith@amazon.de, zide.chen@intel.com, Dongli Zhang , Chenyi Qiang Content-Type: text/plain; charset="us-ascii" On Wed, May 22, 2024, David Woodhouse wrote: > From: David Woodhouse > > Commit d98d07ca7e034 ("KVM: x86: update pvclock area conditionally, on > cpu migration") turned an unconditional KVM_REQ_CLOCK_UPDATE into a > conditional one, if either the master clock isn't enabled *or* the vCPU > was not previously scheduled (vcpu->cpu == -1). The commit message doesn't > explain the latter condition, which is specifically for the master clock > case. It handles the first load of the vCPU, which is distinctly different from CPU migration. > Commit 0061d53daf26f ("KVM: x86: limit difference between kvmclock > updates") later turned that into a KVM_REQ_GLOBAL_CLOCK_UPDATE to avoid > skew between vCPUs. > > In master clock mode there is no need for any of that, regardless of > whether/where this vCPU was previously scheduled. > > Do it only if (!kvm->arch.use_master_clock). > > Signed-off-by: David Woodhouse > --- > arch/x86/kvm/x86.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 32a873d5ed00..dd53860ca284 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -5161,7 +5161,7 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu) > * On a host with synchronized TSC, there is no need to update > * kvmclock on vcpu->cpu migration > */ > - if (!vcpu->kvm->arch.use_master_clock || vcpu->cpu == -1) > + if (!vcpu->kvm->arch.use_master_clock) > kvm_make_request(KVM_REQ_GLOBAL_CLOCK_UPDATE, vcpu); I believe this needs to be: if (!vcpu->kvm->arch.use_master_clock) kvm_make_request(KVM_REQ_GLOBAL_CLOCK_UPDATE, vcpu); else if (vcpu->cpu == -1) kvm_make_request(KVM_REQ_CLOCK_UPDATE, vcpu); or alternatively do KVM_REQ_CLOCK_UPDATE during vCPU creation (hotplug?). > if (vcpu->cpu != cpu) > kvm_make_request(KVM_REQ_MIGRATE_TIMER, vcpu); > -- > 2.44.0 >