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;
MIME-Version: 1.0
References: <20200721041742.197354-1-sergey.senozhatsky@gmail.com>
 <20200817020310.GA1210848@jagdpanzerIV.localdomain> <fe72592c-c721-bece-1469-95eebf931299@huawei.com>
 <cbcfb402b7fdb8a2a45b80fbb0e79f3e@kernel.org> <20200911085841.GB562@jagdpanzerIV.localdomain>
In-Reply-To: <20200911085841.GB562@jagdpanzerIV.localdomain>
From:   Joel Fernandes <joelaf@google.com>
Date:   Tue, 8 Dec 2020 15:02:47 -0500
Message-ID: <CAJWu+oq26OK1-7Ze2pb5xpRJ-tS9wtXOdGFrYpHq+fhkyGhjkA@mail.gmail.com>
Subject: Re: [RFC][PATCH 0/4] arm64:kvm: teach guest sched that VCPUs can be preempted
To:     Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc:     Marc Zyngier <maz@kernel.org>, yezengruan <yezengruan@huawei.com>,
        Will Deacon <will@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Suleiman Souhlal <suleiman@google.com>,
        kvmarm@lists.cs.columbia.edu,
        "moderated list:ARM64 PORT (AARCH64 ARCHITECTURE)" 
        <linux-arm-kernel@lists.infradead.org>,
        "Wanghaibin (D)" <wanghaibin.wang@huawei.com>,
        Quentin Perret <qperret@google.com>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Fri, Sep 11, 2020 at 4:58 AM Sergey Senozhatsky
<sergey.senozhatsky@gmail.com> wrote:
>
> My apologies for the slow reply.
>
> On (20/08/17 13:25), Marc Zyngier wrote:
> >
> > It really isn't the same thing at all. You are exposing PV spinlocks,
> > while Sergey exposes preemption to vcpus.
> >
>
> Correct, we see vcpu preemption as a "fundamental" feature, with
> consequences that affect scheduling, which is a core feature :)
>
> Marc, is there anything in particular that you dislike about this RFC
> patch set? Joel has some ideas, which we may discuss offline if that
> works for you.

Hi Marc, Sergey, Just checking what is the latest on this series?

About the idea me and Sergey discussed, at a high level we discussed
being able to share information similar to "Is the vCPU preempted?"
using a more arch-independent infrastructure. I do not believe this
needs to be arch-specific. Maybe the speciifc mechanism about how to
share a page of information needs to be arch-specific, but the actual
information shared need not be. This could open the door to sharing
more such information in an arch-independent way (for example, if the
scheduler needs to know other information such as the capacity of the
CPU that the vCPU is on).

Other thoughts?

thanks,

 - Joel