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From:   Michael Kelley <mikelley@microsoft.com>
To:     Michael Kelley <mikelley@microsoft.com>,
        Wei Hu <weh@microsoft.com>,
        "rdunlap@infradead.org" <rdunlap@infradead.org>,
        "shc_work@mail.ru" <shc_work@mail.ru>,
        "gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
        "lee.jones@linaro.org" <lee.jones@linaro.org>,
        "alexandre.belloni@bootlin.com" <alexandre.belloni@bootlin.com>,
        "baijiaju1990@gmail.com" <baijiaju1990@gmail.com>,
        "info@metux.net" <info@metux.net>,
        "linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
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        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "sashal@kernel.org" <sashal@kernel.org>,
        Stephen Hemminger <sthemmin@microsoft.com>,
        Haiyang Zhang <haiyangz@microsoft.com>,
        KY Srinivasan <kys@microsoft.com>,
        Dexuan Cui <decui@microsoft.com>
Subject: RE: [PATHC v6] video: hyperv: hyperv_fb: Support deferred IO for
 Hyper-V frame buffer driver
Thread-Topic: [PATHC v6] video: hyperv: hyperv_fb: Support deferred IO for
 Hyper-V frame buffer driver
Thread-Index: AQHVbebF21J2EyXx3k2x6FCXKaeI5qcx+W9wgALZkLA=
Date:   Fri, 20 Sep 2019 17:26:34 +0000
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From: Michael Kelley <mikelley@microsoft.com>  Sent: Wednesday, September 1=
8, 2019 2:48 PM
> >
> > Without deferred IO support, hyperv_fb driver informs the host to refre=
sh
> > the entire guest frame buffer at fixed rate, e.g. at 20Hz, no matter th=
ere
> > is screen update or not. This patch supports deferred IO for screens in
> > graphics mode and also enables the frame buffer on-demand refresh. The
> > highest refresh rate is still set at 20Hz.
> >
> > Currently Hyper-V only takes a physical address from guest as the start=
ing
> > address of frame buffer. This implies the guest must allocate contiguou=
s
> > physical memory for frame buffer. In addition, Hyper-V Gen 2 VMs only
> > accept address from MMIO region as frame buffer address. Due to these
> > limitations on Hyper-V host, we keep a shadow copy of frame buffer
> > in the guest. This means one more copy of the dirty rectangle inside
> > guest when doing the on-demand refresh. This can be optimized in the
> > future with help from host. For now the host performance gain from defe=
rred
> > IO outweighs the shadow copy impact in the guest.
> >
> > Signed-off-by: Wei Hu <weh@microsoft.com>

Sasha -- this patch and one other from Wei Hu for the Hyper-V frame buffer
driver should be ready.  Both patches affect only the Hyper-V frame buffer
driver so can go through the Hyper-V tree.  Can you pick these up?  Thx.

Michael