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

[Alex Bennée <alex.bennee@xxxxxxxxxx>]

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?

FWIW:

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

-- 
Alex Bennée