From mboxrd@z Thu Jan  1 00:00:00 1970
From: Paolo Bonzini <pbonzini@redhat.com>
Subject: Re: vtime accounting
Date: Wed, 15 Mar 2017 09:09:55 +0100
Message-ID: <75e93ee5-348b-7884-3c57-6ad76ef41463@redhat.com>
References: <20170308105700.GA109453@lvm> <20170313162259.GE18298@potion>
 <20170314082601.GC1277@cbox> <20170314165858.GA5435@potion>
 <1d205be1-50ab-59cf-9908-dbbe8c939309@redhat.com>
 <20170314184133.GG1277@cbox> <20170314193201.GC5432@potion>
 <20170314200147.GH1277@cbox> <20170314215229.GE5432@potion>
Mime-Version: 1.0
Content-Type: text/plain; charset=utf-8
Content-Transfer-Encoding: 8bit
Cc: Christoffer Dall <christoffer.dall@linaro.org>,
        kvm@vger.kernel.org, Marc Zyngier <marc.zyngier@arm.com>,
        Rik van Riel <riel@redhat.com>
To: =?UTF-8?B?UmFkaW0gS3LEjW3DocWZ?= <rkrcmar@redhat.com>,
        Christoffer Dall <cdall@linaro.org>
Return-path: <kvm-owner@vger.kernel.org>
Received: from mx1.redhat.com ([209.132.183.28]:41504 "EHLO mx1.redhat.com"
        rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
        id S1751738AbdCOIKE (ORCPT <rfc822;kvm@vger.kernel.org>);
        Wed, 15 Mar 2017 04:10:04 -0400
In-Reply-To: <20170314215229.GE5432@potion>
Sender: kvm-owner@vger.kernel.org
List-ID: <kvm.vger.kernel.org>



On 14/03/2017 22:52, Radim Krčmář wrote:
>> If my statement above about needing interrupts disabled when dealing
>> with vtime, then considering this begins to sound interesting, also
>> given that the vtime thing is not entirely free and we're dealing with
>> the hot path of receiving IPIs here, for example.
> I'm liking it less and less the more I read. :)
> CONTEXT_USER vtime is coupled with context tracking and going out of
> CONTEXT_KERNEL means that RCU cannot be used in between.  Using
> CONTEXT_GUEST from load/put would change the meaning of contexts ...

CONTEXT_GUEST is an RCU extended quiescent state, doing it from load to
put makes no sense.  PF_VCPU from load to put on the other hand might
make some sense.

Paolo