Re: [PATCH] i386: load kernel on xen using DMA

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

On Fri, Jun 18, 2021 at 09:54:14AM +0100, Alex Bennée wrote:
> 
> Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx> writes:
> 
> > Kernel on Xen is loaded via fw_cfg. Previously it used non-DMA version,
> > which loaded the kernel (and initramfs) byte by byte. Change this
> > to DMA, to load in bigger chunks.
> > This change alone reduces load time of a (big) kernel+initramfs from
> > ~10s down to below 1s.
> >
> > This change was suggested initially here:
> > https://lore.kernel.org/xen-devel/20180216204031.000052e9@xxxxxxxxx/
> > Apparently this alone is already enough to get massive speedup.
> >
> > Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>
> > ---
> >  hw/i386/pc.c | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> >
> > diff --git a/hw/i386/pc.c b/hw/i386/pc.c
> > index 8a84b25a03..14e43d4da4 100644
> > --- a/hw/i386/pc.c
> > +++ b/hw/i386/pc.c
> > @@ -839,7 +839,8 @@ void xen_load_linux(PCMachineState *pcms)
> >  
> >      assert(MACHINE(pcms)->kernel_filename != NULL);
> >  
> > -    fw_cfg = fw_cfg_init_io(FW_CFG_IO_BASE);
> > +    fw_cfg = fw_cfg_init_io_dma(FW_CFG_IO_BASE, FW_CFG_IO_BASE + 4,
> > +                                &address_space_memory);
> >      fw_cfg_add_i16(fw_cfg, FW_CFG_NB_CPUS, x86ms->boot_cpus);
> >      rom_set_fw(fw_cfg);
> 
> Gentle ping. The fix looks perfectly sane to me but I don't have any x86
> Xen HW to test this one. Are the x86 maintainers happy to take this on?

Ping...

> 
> FWIW:
> 
> Reviewed-by: Alex Bennée <alex.bennee@xxxxxxxxxx>
> 
> -- 
> Alex Bennée
> 

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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