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

[Anthony PERARD <anthony.perard@xxxxxxxxx>]

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?

Yes. It looks like it works well with both SeaBIOS and OVMF, so the
patch is good.

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

Reviewed-by: Anthony PERARD <anthony.perard@xxxxxxxxxx>

Thanks,

-- 
Anthony PERARD