linux-kernel - RE: [PATCH v5] video: hyperv: hyperv_fb: Support deferred IO for Hyper-V frame buffer driver

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Date:   Wed, 2 Oct 2019 07:52:27 +0000
From:   Dexuan Cui <decui@...rosoft.com>
To:     Sasha Levin <sashal@...nel.org>, Wei Hu <weh@...rosoft.com>
CC:     Michael Kelley <mikelley@...rosoft.com>,
        "rdunlap@...radead.org" <rdunlap@...radead.org>,
        "shc_work@...l.ru" <shc_work@...l.ru>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "lee.jones@...aro.org" <lee.jones@...aro.org>,
        "alexandre.belloni@...tlin.com" <alexandre.belloni@...tlin.com>,
        "baijiaju1990@...il.com" <baijiaju1990@...il.com>,
        "fthain@...egraphics.com.au" <fthain@...egraphics.com.au>,
        "info@...ux.net" <info@...ux.net>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        KY Srinivasan <kys@...rosoft.com>
Subject: RE: [PATCH v5] video: hyperv: hyperv_fb: Support deferred IO for
 Hyper-V frame buffer driver

> From: Sasha Levin <sashal@...nel.org>
> Sent: Tuesday, October 1, 2019 11:45 AM
> To: Wei Hu <weh@...rosoft.com>
> 
> On Fri, Sep 13, 2019 at 06:02:55AM +0000, Wei Hu wrote:
> >Without deferred IO support, hyperv_fb driver informs the host to refresh
> >the entire guest frame buffer at fixed rate, e.g. at 20Hz, no matter there
> >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 starting
> >address of frame buffer. This implies the guest must allocate contiguous
> >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 deferred
> >IO outweighs the shadow copy impact in the guest.
> >
> >Signed-off-by: Wei Hu <weh@...rosoft.com>
> 
> What tree is this based on? I can't get it to apply.
> 
> Thanks,
> Sasha

Please use Wei's v6 patch, which can apply on today's hyperv/linux.git/s hyperv-next branch.

Thanks,
-- Dexuan