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Re: [Qemu-devel] [RFC PATCH v2 00/12] Guest startup time optimization
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [RFC PATCH v2 00/12] Guest startup time optimization |
Date: |
Mon, 5 Sep 2016 05:37:00 +0300 |
On Fri, Sep 02, 2016 at 01:08:29PM +0200, Paolo Bonzini wrote:
>
>
> On 25/08/2016 12:14, Chao Peng wrote:
> > This patchset is trying to optimize guest startup time by disabling
> > or simplifying some features in QEMU. The version 1 can be found at:
> > https://lists.nongnu.org/archive/html/qemu-devel/2016-06/msg04842.html
> >
> > Unlike version 1, this version optimizes Q35 directly instead of
> > introducing a totally new platform. But we still keep the design of
> > skipping firmware as till now we don't have good idea to optimize
> > firmware to get the comparable boot time.
> >
> > The patchset is against commit 5f0e775 (Update version for v2.7.0-rc3
> > release) on master branch.
> >
> > Basically this patchset introduces several switches to qemu comandline
> > so that several features can be turned off in some use cases. The
> > default behavior will not change in case no switches are provided.
> >
> > Performance data:
> > feature(switches) time saved in guest
> > -nosmbus 4ms
> > -nosata 6ms
> > -nopic 2ms
> > -nopit 5ms
> > -static-prt 8ms
> > -nofw 62ms
> >
> > Thanks,
> > Chao
> >
> > Chao Peng (9):
> > pc: make smbus configurable
> > pc: make sata configurable
> > pc: make pic configurable
> > pc: make pit configurable
> > acpi: build static _PRT
> > ich9: enable pm registers when there is no firmware
> > q35: initialize MMCFG base when there is no firmware
> > pc: support direct loading protected/long mode kernel
> > pc: skip firmware
> >
> > Haozhong Zhang (3):
> > acpi: expose data structurs and functions of BIOS linker loader
> > acpi: expose acpi_checksum()
> > acpi: patch guest ACPI when there is no firmware
> >
> > hw/acpi/bios-linker-loader.c | 83 +---------
> > hw/acpi/core.c | 2 +-
> > hw/acpi/nvdimm.c | 6 +-
> > hw/i386/Makefile.objs | 2 +-
> > hw/i386/acpi-build-nofw.c | 295
> > ++++++++++++++++++++++++++++++++++
> > hw/i386/acpi-build.c | 102 +++++++-----
> > hw/i386/acpi-build.h | 5 +
> > hw/i386/pc.c | 301
> > +++++++++++++++++++++++++++++++----
> > hw/i386/pc_piix.c | 2 +-
> > hw/i386/pc_q35.c | 60 ++++---
> > hw/isa/lpc_ich9.c | 12 +-
> > hw/pci-host/q35.c | 15 +-
> > include/hw/acpi/acpi.h | 2 +
> > include/hw/acpi/bios-linker-loader.h | 85 ++++++++++
> > include/hw/i386/pc.h | 16 +-
> > 15 files changed, 800 insertions(+), 188 deletions(-)
> > create mode 100644 hw/i386/acpi-build-nofw.c
>
> Patches 1-4 are okay, though I think it would be easier to add a -M
> q35-lite too that just removes the legacy devices. The -M q35-lite
> machine doesn't have to support versioning for now.
Where q35-lite will be same as q35 with different defaults?
Sure, I don't have a problem with this.
In particular this will allow things like "q35-lite but with sata" etc.
> As you might expect, I don't agree with removing the firmware. There's
> room for much more optimization before duplicating firmware code in
> QEMU. I'd rather see numbers for:
>
> 1) qboot optimizations: adopt the fw_cfg DMA interface instead of the
> cbfs flash hack (so that -kernel works), drop PCI bridge initialization,
> copy less than 64K of memory from ROM to 0xf0000;
>
> 2) Linux optimizations: using an uncompressed image to avoid the cost of
> copying and decompressing. QEMU can already load the image at the right
> place and the real mode stub can do little more than GDT/IDT setup.
>
> 3) PAM optimizations: for -M q35-lite initialize the machine with RAM
> from 0xc0000 to 1MB.
>
> I know that you ultimately would like to mmap the kernel, but I would
> like to have a better understanding of where the time is spent.
>
> Thanks,
>
> Paolo