From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Matlack Date: Tue, 28 Sep 2021 22:08:33 +0000 Subject: Re: [PATCH 12/14] KVM: Don't redo ktime_get() when calculating halt-polling stop/deadline Message-Id: List-Id: References: <20210925005528.1145584-1-seanjc@google.com> <20210925005528.1145584-13-seanjc@google.com> In-Reply-To: <20210925005528.1145584-13-seanjc@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Sean Christopherson Cc: Marc Zyngier , Huacai Chen , Aleksandar Markovic , Paul Mackerras , Christian Borntraeger , Janosch Frank , Paolo Bonzini , James Morse , Alexandru Elisei , Suzuki K Poulose , David Hildenbrand , Cornelia Huck , Claudio Imbrenda , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-mips@vger.kernel.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, linux-kernel@vger.kernel.org, Jing Zhang On Fri, Sep 24, 2021 at 05:55:26PM -0700, Sean Christopherson wrote: > Calculate the halt-polling "stop" time using "cur" instead of redoing > ktime_get(). In the happy case where hardware correctly predicts > do_halt_poll, "cur" is only a few cycles old. And if the branch is > mispredicted, arguably that extra latency should count toward the > halt-polling time. > > In all likelihood, the numbers involved are in the noise and either > approach is perfectly ok. > > Signed-off-by: Sean Christopherson Reviewed-by: David Matlack > --- > virt/kvm/kvm_main.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index 2980d2b88559..80f78daa6b8d 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -3267,7 +3267,7 @@ void kvm_vcpu_halt(struct kvm_vcpu *vcpu) > > start = cur = poll_end = ktime_get(); > if (do_halt_poll) { > - ktime_t stop = ktime_add_ns(ktime_get(), vcpu->halt_poll_ns); > + ktime_t stop = ktime_add_ns(cur, vcpu->halt_poll_ns); > > do { > /* > -- > 2.33.0.685.g46640cef36-goog > From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C5789C433FE for ; Wed, 29 Sep 2021 07:12:50 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id 7BA0A6137E for ; Wed, 29 Sep 2021 07:12:50 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 7BA0A6137E Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=lists.cs.columbia.edu Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 27A214B0F1; Wed, 29 Sep 2021 03:12:50 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Authentication-Results: mm01.cs.columbia.edu (amavisd-new); dkim=softfail (fail, message has been altered) header.i=@google.com Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 1FfJSIqNuXtK; Wed, 29 Sep 2021 03:12:48 -0400 (EDT) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 024604B15E; Wed, 29 Sep 2021 03:12:42 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 779994048A for ; Tue, 28 Sep 2021 18:08:39 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id URRBhaZWcfax for ; Tue, 28 Sep 2021 18:08:38 -0400 (EDT) Received: from mail-pf1-f170.google.com (mail-pf1-f170.google.com [209.85.210.170]) by mm01.cs.columbia.edu (Postfix) with ESMTPS id 7BB3640191 for ; Tue, 28 Sep 2021 18:08:38 -0400 (EDT) Received: by mail-pf1-f170.google.com with SMTP id w19so185787pfn.12 for ; Tue, 28 Sep 2021 15:08:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=7rZGZtXj4Kjef8XTrbQn+IEWHZmecIVKI32pSog3bGg=; b=Gu0/C+e+W8WPTJ9kWJuQrZyoELFPICJgw72WckzL3ovfDopNe/Y4j2IPagVtUNhWwr 9Qjfpn7SXH4wDFaqEdg5HJLXeLxphcPK9HcAugMDnWCpp68Xe6/ys1kzGwvSk+KcGCM4 H64DJ7Tp5uRS7wp3aWTm1GhwRjDkRVaP2QPSIltqiZGDJzmU5Y11dt/buGH/9lHZ3SWJ bNi0rTAatQvQMs/Fb32BQ7aRL6utqOVWshzHxUOyBU70FP8VoWG62/RzZsJ4kBiRc9ua EQxp57U7HkBAHrtePs5fCEn33r7qnlM/POKA5AQ8Js4rYnMiBHo1lKgjrUm4AiUxx6TO BFlA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=7rZGZtXj4Kjef8XTrbQn+IEWHZmecIVKI32pSog3bGg=; b=gwjDO9wXllbwRiNwCW2EvnCXuQLRNbrK4cs72kb0ulyFY8KOJJdUB7nhGAGBnmyHth lsvanqmNwBLmiFGgbRg3sr9eC6lSPuN8oQbbrOwKjAGnXE6MwE9TdSXNrv0y6HJSO3o6 eyUdgIEck2MCZ2VC8LvNdyBPkCZ4OMuYCAx4bvJUCu7tCY64bhI0X3yZ78CCpFJqrWhi wQ8fIvedTiFPyCuviEekzLvzuYVuBmgiyy/0SrNj0ttSgYlpCmqVxjsQaDK0TUc4Ylem HFLIAFn5ePMHPQYwhfwS2cUGYZW/SMB1llap7lmx3Aj6dB4CbtOhNN7ATrH+ZDngsIky nNFA== X-Gm-Message-State: AOAM5301BQx6I/MIja5QGr8yyJdnso0HD5A1O0Kt6KnCITqJRFLCgsXC OH0lFT36jcXmh6TPSAHwZBca9Q== X-Google-Smtp-Source: ABdhPJzadyVUO8UyxBHsA0YYc+iUIbEvRB9U2t+kYPdczvOjLMgOq7SgcZR4mYDt3YnbOWn2xcwTMQ== X-Received: by 2002:a05:6a00:26cc:b0:440:51c6:fa38 with SMTP id p12-20020a056a0026cc00b0044051c6fa38mr7862566pfw.45.1632866917363; Tue, 28 Sep 2021 15:08:37 -0700 (PDT) Received: from google.com (254.80.82.34.bc.googleusercontent.com. [34.82.80.254]) by smtp.gmail.com with ESMTPSA id v6sm132638pfv.83.2021.09.28.15.08.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 28 Sep 2021 15:08:36 -0700 (PDT) Date: Tue, 28 Sep 2021 22:08:33 +0000 From: David Matlack To: Sean Christopherson Subject: Re: [PATCH 12/14] KVM: Don't redo ktime_get() when calculating halt-polling stop/deadline Message-ID: References: <20210925005528.1145584-1-seanjc@google.com> <20210925005528.1145584-13-seanjc@google.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210925005528.1145584-13-seanjc@google.com> X-Mailman-Approved-At: Wed, 29 Sep 2021 03:12:40 -0400 Cc: Wanpeng Li , kvm@vger.kernel.org, David Hildenbrand , linux-kernel@vger.kernel.org, Paul Mackerras , Claudio Imbrenda , kvmarm@lists.cs.columbia.edu, Janosch Frank , Marc Zyngier , Joerg Roedel , Huacai Chen , Christian Borntraeger , Aleksandar Markovic , kvm-ppc@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Jim Mattson , Cornelia Huck , linux-mips@vger.kernel.org, Paolo Bonzini , Vitaly Kuznetsov X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu On Fri, Sep 24, 2021 at 05:55:26PM -0700, Sean Christopherson wrote: > Calculate the halt-polling "stop" time using "cur" instead of redoing > ktime_get(). In the happy case where hardware correctly predicts > do_halt_poll, "cur" is only a few cycles old. And if the branch is > mispredicted, arguably that extra latency should count toward the > halt-polling time. > > In all likelihood, the numbers involved are in the noise and either > approach is perfectly ok. > > Signed-off-by: Sean Christopherson Reviewed-by: David Matlack > --- > virt/kvm/kvm_main.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index 2980d2b88559..80f78daa6b8d 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -3267,7 +3267,7 @@ void kvm_vcpu_halt(struct kvm_vcpu *vcpu) > > start = cur = poll_end = ktime_get(); > if (do_halt_poll) { > - ktime_t stop = ktime_add_ns(ktime_get(), vcpu->halt_poll_ns); > + ktime_t stop = ktime_add_ns(cur, vcpu->halt_poll_ns); > > do { > /* > -- > 2.33.0.685.g46640cef36-goog > _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 7B826C433EF for ; Tue, 28 Sep 2021 22:11:01 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 400286137A for ; Tue, 28 Sep 2021 22:11:01 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.4.1 mail.kernel.org 400286137A Authentication-Results: mail.kernel.org; dmarc=fail (p=reject dis=none) header.from=google.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20210309; h=Sender: Content-Transfer-Encoding:Content-Type:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:Cc:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=mHd9D9J03Rv/Wfn6MqbU1BzF4zBx2SFMB5v1nSoP+NY=; b=Udx+p3nT+fx0tK V6XuFQiOfD7J5J6yZarWOmYYNXxGqE5xpV67CAlTppSVr2e/aOWppcMs1tMGkVztol+/Tq8V9RjNJ Z1wXTKPIpM5iUUMZENM4QkPC+39me2KpjJCopc8QOdYF2dBhfRHRf1b436WfyVaKuJggI8f3RWf+H eoTN3D06QW8ebj1SKDIS6JlD36S6vCCgNM2uq+tPJQNVFig7sWmvkTAnaQb0dV0a8TM6YLyrask8N VGJBtsJ5A0MAAthd4QN5Zb/7vRAm/325LzIpFLBcbkTsfhUSLyHgmFwfu6NbWt7kefdQ7NNKcI8kg RJzF2GNf8Pg9glAO6eMw==; Received: from localhost ([::1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.94.2 #2 (Red Hat Linux)) id 1mVLHL-008yP6-En; Tue, 28 Sep 2021 22:08:48 +0000 Received: from mail-pf1-x435.google.com ([2607:f8b0:4864:20::435]) by bombadil.infradead.org with esmtps (Exim 4.94.2 #2 (Red Hat Linux)) id 1mVLHG-008yMV-20 for linux-arm-kernel@lists.infradead.org; Tue, 28 Sep 2021 22:08:43 +0000 Received: by mail-pf1-x435.google.com with SMTP id b68so193211pfb.10 for ; Tue, 28 Sep 2021 15:08:38 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=7rZGZtXj4Kjef8XTrbQn+IEWHZmecIVKI32pSog3bGg=; b=Gu0/C+e+W8WPTJ9kWJuQrZyoELFPICJgw72WckzL3ovfDopNe/Y4j2IPagVtUNhWwr 9Qjfpn7SXH4wDFaqEdg5HJLXeLxphcPK9HcAugMDnWCpp68Xe6/ys1kzGwvSk+KcGCM4 H64DJ7Tp5uRS7wp3aWTm1GhwRjDkRVaP2QPSIltqiZGDJzmU5Y11dt/buGH/9lHZ3SWJ bNi0rTAatQvQMs/Fb32BQ7aRL6utqOVWshzHxUOyBU70FP8VoWG62/RzZsJ4kBiRc9ua EQxp57U7HkBAHrtePs5fCEn33r7qnlM/POKA5AQ8Js4rYnMiBHo1lKgjrUm4AiUxx6TO BFlA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=7rZGZtXj4Kjef8XTrbQn+IEWHZmecIVKI32pSog3bGg=; b=tTeJAXgNC6Sx2JrgdpgI91heTJZfDjH6y5fROQbZIKvB6sfVG0xtNnplF/8o9BnwYz dNclIbZKX3kYbkH+IW4l4hnfwXAY28tn+ckXOmvAjIurrwZVjQq3APxLq8Rb017VMVEx mC5GRxm2c8O6Z38dUoEQLHvz8OWJAnNBQxpB/qwaSQu4nNSvgH6d32rDxoD08wRfgdbC a7ln0nSeb12Xa20whUnzCdCPoh/tRJDY2jbF0JMdtuLf3MNMNaUko/Om3vjKlQu7KPxp RqcR+z5C27bi+DBrtzaOrdLBFtpi31KLptXxezunpCu0xOV08TQo6gSF03Si2GL2FFi4 FwfA== X-Gm-Message-State: AOAM533eGW3yyTkFdMtrpYYi9BNWnGs/6kqasm/pfXM8Fp6LBjAH2LvL xJPCqXIxoVL98wuTEYpc93kZlg== X-Google-Smtp-Source: ABdhPJzadyVUO8UyxBHsA0YYc+iUIbEvRB9U2t+kYPdczvOjLMgOq7SgcZR4mYDt3YnbOWn2xcwTMQ== X-Received: by 2002:a05:6a00:26cc:b0:440:51c6:fa38 with SMTP id p12-20020a056a0026cc00b0044051c6fa38mr7862566pfw.45.1632866917363; Tue, 28 Sep 2021 15:08:37 -0700 (PDT) Received: from google.com (254.80.82.34.bc.googleusercontent.com. [34.82.80.254]) by smtp.gmail.com with ESMTPSA id v6sm132638pfv.83.2021.09.28.15.08.36 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 28 Sep 2021 15:08:36 -0700 (PDT) Date: Tue, 28 Sep 2021 22:08:33 +0000 From: David Matlack To: Sean Christopherson Cc: Marc Zyngier , Huacai Chen , Aleksandar Markovic , Paul Mackerras , Christian Borntraeger , Janosch Frank , Paolo Bonzini , James Morse , Alexandru Elisei , Suzuki K Poulose , David Hildenbrand , Cornelia Huck , Claudio Imbrenda , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-mips@vger.kernel.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, linux-kernel@vger.kernel.org, Jing Zhang Subject: Re: [PATCH 12/14] KVM: Don't redo ktime_get() when calculating halt-polling stop/deadline Message-ID: References: <20210925005528.1145584-1-seanjc@google.com> <20210925005528.1145584-13-seanjc@google.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210925005528.1145584-13-seanjc@google.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210928_150842_134396_908309FB X-CRM114-Status: GOOD ( 20.67 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Fri, Sep 24, 2021 at 05:55:26PM -0700, Sean Christopherson wrote: > Calculate the halt-polling "stop" time using "cur" instead of redoing > ktime_get(). In the happy case where hardware correctly predicts > do_halt_poll, "cur" is only a few cycles old. And if the branch is > mispredicted, arguably that extra latency should count toward the > halt-polling time. > > In all likelihood, the numbers involved are in the noise and either > approach is perfectly ok. > > Signed-off-by: Sean Christopherson Reviewed-by: David Matlack > --- > virt/kvm/kvm_main.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > index 2980d2b88559..80f78daa6b8d 100644 > --- a/virt/kvm/kvm_main.c > +++ b/virt/kvm/kvm_main.c > @@ -3267,7 +3267,7 @@ void kvm_vcpu_halt(struct kvm_vcpu *vcpu) > > start = cur = poll_end = ktime_get(); > if (do_halt_poll) { > - ktime_t stop = ktime_add_ns(ktime_get(), vcpu->halt_poll_ns); > + ktime_t stop = ktime_add_ns(cur, vcpu->halt_poll_ns); > > do { > /* > -- > 2.33.0.685.g46640cef36-goog > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel