Alexey Kardashevskiy <a...@ozlabs.ru> writes:
> At the moment, on 256CPU + 256 PCI devices guest, it takes the guest
> about 8.5sec to read the entire device tree. Some explanation can be
> found here: https://patchwork.ozlabs.org/patch/826124/ but mostly it is
> because the kernel traverses the tree twice and it calls "getprop" for
> each properly which is really SLOF as it searches from the linked list
> beginning every time.
>
> Since SLOF has just learned to build FDT and this takes less than 0.5sec
> for such a big guest, this makes use of the proposed client interface
> method - "fdt-fetch".
It's a pity doing it the normal way is so slow, but this seems like a
reasonable idea anyway.
> diff --git a/arch/powerpc/kernel/prom_init.c b/arch/powerpc/kernel/prom_init.c
> index 02190e90c7ae..daa50a153737 100644
> --- a/arch/powerpc/kernel/prom_init.c
> +++ b/arch/powerpc/kernel/prom_init.c
> @@ -2498,6 +2498,31 @@ static void __init flatten_device_tree(void)
> prom_panic("Can't allocate initial device-tree chunk\n");
> mem_end = mem_start + room;
I'd prefer you didn't munge it inside flatten_device_tree(), rather
create a wrapper that does ~=:
void get_flat_devicetree(void)
{
if (!fetch_flat_devicetree())
flatten_device_tree();
printf(...)
}
> + if (!call_prom_ret("fdt-fetch", 2, 1, NULL, mem_start,
> + room - sizeof(mem_reserve_map))) {
> + u32 size;
> +
> + hdr = (void *) mem_start;
> +
> + /* Fixup the boot cpuid */
> + hdr->boot_cpuid_phys = cpu_to_be32(prom.cpu);
> +
> + /* Append the reserved map to the end of the blob */
> + hdr->off_mem_rsvmap = hdr->totalsize;
> + size = be32_to_cpu(hdr->totalsize);
> + rsvmap = (void *) hdr + size;
> + hdr->totalsize = cpu_to_be32(size + sizeof(mem_reserve_map));
> + memcpy(rsvmap, mem_reserve_map, sizeof(mem_reserve_map));
> +
> + /* Store the DT address */
> + dt_header_start = mem_start;
> +
> +#ifdef DEBUG_PROM
> + prom_printf("Fetched DTB: %d bytes to @%x\n", size, mem_start);
> +#endif
I think that should actually not be under DEBUG_PROM. The origin of the
FDT is fairly crucial information, so I think we can tolerate an extra
line of output to know that.
> + goto print_exit;
This was the clue that it should be in a separate function :)
cheers
> + }
> +
> /* Get root of tree */
> root = call_prom("peer", 1, 1, (phandle)0);
> if (root == (phandle)0)
> @@ -2548,6 +2573,7 @@ static void __init flatten_device_tree(void)
> /* Copy the reserve map in */
> memcpy(rsvmap, mem_reserve_map, sizeof(mem_reserve_map));
>
> +print_exit:
> #ifdef DEBUG_PROM
> {
> int i;
> --
> 2.11.0
