Re: [Qemu-devel] [PATCH v4] Add optionrom compatible with fw_cfg DMA version

[Stefan Hajnoczi]

On Mon, Feb 22, 2016 at 02:56:27PM +0300, Vladimir Sementsov-Ogievskiy wrote:
> Hi, Marc!
> 
> Am I right, that this patch is necessary to reproduce your results from
> "QEMU fw_cfg DMA interface"?
> 
> >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
> 
> Because, without this patch seabios (and independently of your other
> patches) calls linuxboot optionrom, which loads kernel through io-ports
> (It's in pc-bios/optionrom/linuxboot.S:
> "read_fw_blob_addr32(FW_CFG_KERNEL)"), and this reading is the most
> time-spending part of "Kernel setup" phase.
> 
> Am I missing something?

Yes, this patch makes -kernel/-initrd use fw_cfg DMA.

Stefan

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