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From: =?UTF-8?q?Marc=20Mar=C3=AD?= <markmb@redhat.com>
Date: Thu,  6 Aug 2015 13:00:16 +0200
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Subject: [Qemu-devel] QEMU fw_cfg DMA interface
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To: linux-kernel@vger.kernel.org, qemu-devel@nongnu.org, seabios@seabios.org
Cc: Drew <drjones@redhat.com>, Stefan Hajnoczi <stefanha@gmail.com>, Kevin O'Connor <kevin@koconnor.net>, Gerd Hoffmann <kraxel@redhat.com>, =?UTF-8?q?Marc=20Mar=C3=AD?= <markmb@redhat.com>, Laszlo <lersek@redhat.com>

Implementation of the FW CFG DMA interface.

When running a Linux guest on top of QEMU, using the -kernel options, thi=
s
is the timing improvement for x86:

QEMU commit 2be4f242b50a8 and SeaBIOS commit 908a58c1d5ff
QEMU startup time: .078
BIOS startup time: .060
Kernel setup time: .578
Total time: .716

QEMU with this patch series and SeaBIOS with this patch series
QEMU startup time: .080
BIOS startup time: .039
Kernel setup time: .002
Total time: .121

QEMU startup time is the time between the start and the first kvm_entry.
BIOS startup time is the time between the first kvm_entry and the start o=
f
function do_boot, in SeaBIOS.
Kernel setup time is the time between the start of the function do_boot i=
n
SeaBIOS and the jump to the Linux kernel.

As you can see, both the BIOS (because of ACPI tables and other configura=
tions)
and the Linux kernel boot (because of the copy to memory) are greatly
improved with this new interface.

Also, this new interface is an addon to the old interface. Both interface=
s
are compatible and interchangeable.