Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Wed, 17 Oct 2018 11:08:57 +0100
From:   Stefan Hajnoczi <stefanha@gmail.com>
To:     Peng Hao <peng.hao2@zte.com.cn>
Cc:     pbonzini@redhat.com, rkrcmar@redhat.com,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org
Subject: Re: [PATCH V5 0/3] introduce coalesced pio support
Message-ID: <20181017100857.GN22755@stefanha-x1.localdomain>
References: <1539472197-111085-1-git-send-email-peng.hao2@zte.com.cn>
MIME-Version: 1.0
Content-Type: multipart/signed; micalg=pgp-sha1;
        protocol="application/pgp-signature"; boundary="4Y142/9l9nQlBiaj"
Content-Disposition: inline
In-Reply-To: <1539472197-111085-1-git-send-email-peng.hao2@zte.com.cn>
User-Agent: Mutt/1.10.1 (2018-07-13)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


--4Y142/9l9nQlBiaj
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
Content-Transfer-Encoding: quoted-printable

On Sun, Oct 14, 2018 at 07:09:54AM +0800, Peng Hao wrote:
> Coalesced pio is based on coalesced mmio and can be used for some port
> like rtc port, pci-host config port and so on.
>=20
> Specially in case of rtc as coalesced pio, some versions of windows guest
> access rtc frequently because of rtc as system tick. guest access rtc like
> this: write register index to 0x70, then write or read data from 0x71.
> writing 0x70 port is just as index and do nothing else. So we can use
> coalesced pio to handle this scene to reduce VM-EXIT time.
>=20
> When starting and closing a virtual machine, it will access pci-host conf=
ig
> port frequently. So setting these port as coalesced pio can reduce startu=
p=20
> and shutdown time.=20
>=20
> without my patch, get the vm-exit time of accessing rtc 0x70 and piix 0xc=
f8
> using perf tools: (guest OS : windows 7 64bit)
> IO Port Access  Samples Samples%  Time%  Min Time  Max Time  Avg time
> 0x70:POUT        86     30.99%    74.59%   9us      29us    10.75us (+- 3=
=2E41%)
> 0xcf8:POUT     1119     2.60%     2.12%   2.79us    56.83us 3.41us (+- 2.=
23%)
>=20
> with my patch
> IO Port Access  Samples Samples%  Time%   Min Time  Max Time   Avg time
> 0x70:POUT       106    32.02%    29.47%    0us      10us     1.57us (+- 7=
=2E38%)
> 0xcf8:POUT      1065    1.67%     0.28%   0.41us    65.44us   0.66us (+- =
10.55%)
>=20
>=20
> Peng Hao (3):
>   kvm/x86 : add coalesced pio support
>   kvm/x86 : add document for coalesced mmio
>   kvm/x86 : add document for coalesced pio
>=20
>  Documentation/virtual/kvm/api.txt             | 28 +++++++++++++++++++++=
++++++
>  include/uapi/linux/kvm.h                      | 11 +++++++++--
>  virt/kvm/coalesced_mmio.c                     | 12 +++++++++---
>  virt/kvm/kvm_main.c                           |  2 ++
>  4 files changed, 48 insertions(+), 5 deletions(-)

Nice, thanks for documenting the API!

--4Y142/9l9nQlBiaj
Content-Type: application/pgp-signature; name="signature.asc"

-----BEGIN PGP SIGNATURE-----

iQEcBAEBAgAGBQJbxwo5AAoJEJykq7OBq3PIH10IAMaApryCx6v0aQ0WbgvmZb/8
gO0uSxCKj9L/O4QEAk4C5cv5mmN8qiTnXl21UTPlVeBTUXN2CyNjJc+rEM9r/0k3
YGM281yxB8uNQuGHh1psGFieWRLCvbA/eJSJEHKr3l8JGA/6UwcaWvdtkVMkD4Ps
J8Q8IuiyXIRZBUh8+QlcoHg4J8C1ouopNzl+HzeMSfK6nrbAu6f/9x+DB2ePlqQK
w1SXq3jlzyHTIHmestFpAxZV/I+Tu/nMkvFhRisqzIqJe3v1r+p94YGU0qY2bWP0
kM++MqVM3ujgMvQ6M1gdVLmJ5QW9vI4JNYKMfYB31MESCArOVOk6fd/JpoduelY=
=xifU
-----END PGP SIGNATURE-----

--4Y142/9l9nQlBiaj--