linux-fbdev.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Wei Liu <wei.liu@kernel.org>
To: Michael Kelley <mikelley@microsoft.com>
Cc: Dexuan Cui <decui@microsoft.com>,
	KY Srinivasan <kys@microsoft.com>,
	Haiyang Zhang <haiyangz@microsoft.com>,
	Stephen Hemminger <sthemmin@microsoft.com>,
	"wei.liu@kernel.org" <wei.liu@kernel.org>,
	"b.zolnierkie@samsung.com" <b.zolnierkie@samsung.com>,
	"linux-hyperv@vger.kernel.org" <linux-hyperv@vger.kernel.org>,
	"dri-devel@lists.freedesktop.org"
	<dri-devel@lists.freedesktop.org>,
	"linux-fbdev@vger.kernel.org" <linux-fbdev@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Wei Hu <weh@microsoft.com>
Subject: Re: [PATCH] video: hyperv_fb: Fix the cache type when mapping the VRAM
Date: Wed, 18 Nov 2020 09:31:53 +0000	[thread overview]
Message-ID: <20201118093153.irs3i342nskkbuil@liuwe-devbox-debian-v2> (raw)
In-Reply-To: <MW2PR2101MB105243C3AD5106B2ABEDBAB5D7E10@MW2PR2101MB1052.namprd21.prod.outlook.com>

On Wed, Nov 18, 2020 at 12:20:11AM +0000, Michael Kelley wrote:
> From: Dexuan Cui <decui@microsoft.com> Sent: Tuesday, November 17, 2020 4:03 PM
> > 
> > x86 Hyper-V used to essentially always overwrite the effective cache type
> > of guest memory accesses to WB. This was problematic in cases where there
> > is a physical device assigned to the VM, since that often requires that
> > the VM should have control over cache types. Thus, on newer Hyper-V since
> > 2018, Hyper-V always honors the VM's cache type, but unexpectedly Linux VM
> > users start to complain that Linux VM's VRAM becomes very slow, and it
> > turns out that Linux VM should not map the VRAM uncacheable by ioremap().
> > Fix this slowness issue by using ioremap_cache().
> > 
> > On ARM64, ioremap_cache() is also required as the host also maps the VRAM
> > cacheable, otherwise VM Connect can't display properly with ioremap() or
> > ioremap_wc().
> > 
> > With this change, the VRAM on new Hyper-V is as fast as regular RAM, so
> > it's no longer necessary to use the hacks we added to mitigate the
> > slowness, i.e. we no longer need to allocate physical memory and use
> > it to back up the VRAM in Generation-1 VM, and we also no longer need to
> > allocate physical memory to back up the framebuffer in a Generation-2 VM
> > and copy the framebuffer to the real VRAM. A further big change will
> > address these for v5.11.
> > 
> > Fixes: 68a2d20b79b1 ("drivers/video: add Hyper-V Synthetic Video Frame Buffer Driver")
> > Tested-by: Boqun Feng <boqun.feng@gmail.com>
> > Signed-off-by: Dexuan Cui <decui@microsoft.com>
> Reviewed-by: Michael Kelley <mikelley@microsoft.com>
> 

Applied to hyperv-fixes. Thanks.

  reply	other threads:[~2020-11-18  9:32 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-18  0:03 [PATCH] video: hyperv_fb: Fix the cache type when mapping the VRAM Dexuan Cui
2020-11-18  0:20 ` Michael Kelley
2020-11-18  9:31   ` Wei Liu [this message]
2020-11-18 21:10 ` Haiyang Zhang

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=20201118093153.irs3i342nskkbuil@liuwe-devbox-debian-v2 \
    --to=wei.liu@kernel.org \
    --cc=b.zolnierkie@samsung.com \
    --cc=decui@microsoft.com \
    --cc=dri-devel@lists.freedesktop.org \
    --cc=haiyangz@microsoft.com \
    --cc=kys@microsoft.com \
    --cc=linux-fbdev@vger.kernel.org \
    --cc=linux-hyperv@vger.kernel.org \
    --cc=linux-kernel@vger.kernel.org \
    --cc=mikelley@microsoft.com \
    --cc=sthemmin@microsoft.com \
    --cc=weh@microsoft.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).