linux-kernel - Re: [PATCH v3 00/21] KVM: Dirty ring interface

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Date:   Thu, 9 Jan 2020 11:17:42 -0500
From:   Peter Xu <peterx@...hat.com>
To:     "Michael S. Tsirkin" <mst@...hat.com>
Cc:     kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Christophe de Dinechin <dinechin@...hat.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Yan Zhao <yan.y.zhao@...el.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Jason Wang <jasowang@...hat.com>,
        Kevin Kevin <kevin.tian@...el.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        "Dr . David Alan Gilbert" <dgilbert@...hat.com>
Subject: Re: [PATCH v3 00/21] KVM: Dirty ring interface

On Thu, Jan 09, 2020 at 10:59:50AM -0500, Michael S. Tsirkin wrote:
> On Thu, Jan 09, 2020 at 09:57:08AM -0500, Peter Xu wrote:
> > Branch is here: https://github.com/xzpeter/linux/tree/kvm-dirty-ring
> > (based on kvm/queue)
> > 
> > Please refer to either the previous cover letters, or documentation
> > update in patch 12 for the big picture.
> 
> I would rather you pasted it here. There's no way to respond otherwise.

Sure, will do in the next post.

> 
> For something that's presumably an optimization, isn't there
> some kind of testing that can be done to show the benefits?
> What kind of gain was observed?

Since the interface seems to settle soon, maybe it's time to work on
the QEMU part so I can give some number.  It would be interesting to
know the curves between dirty logging and dirty ring even for some
small vms that have some workloads inside.

> 
> I know it's mostly relevant for huge VMs, but OTOH these
> probably use huge pages.

Yes huge VMs could benefit more, especially if the dirty rate is not
that high, I believe.  Though, could you elaborate on why huge pages
are special here?

Thanks,

-- 
Peter Xu