On Wed, May 01, 2019 at 01:42:21PM +1000, Alexey Kardashevskiy wrote: > At the moment, on 256CPU + 256 PCI devices guest, it takes the guest > about 8.5sec to fetch the entire device tree via the client interface > as the DT is traversed twice - for strings blob and for struct blob. > Also, "getprop" is quite slow too as SLOF stores properties in a linked > list. > > However, since [1] SLOF builds flattened device tree (FDT) for another > purpose. [2] adds a new "fdt-fetch" client interface for the OS to fetch > the FDT. > > This tries the new method; if not supported, this falls back to > the old method. > > There is a change in the FDT layout - the old method produced > (reserved map, strings, structs), the new one receives only strings and > structs from the firmware and adds the final reserved map to the end, > so it is (fw reserved map, strings, structs, reserved map). > This still produces the same unflattened device tree. > > This merges the reserved map from the firmware into the kernel's reserved > map. At the moment SLOF generates an empty reserved map so this does not > change the existing behaviour in regard of reservations. > > This supports only v17 onward as only that version provides dt_struct_size > which works as "fdt-fetch" only produces v17 blobs. > > If "fdt-fetch" is not available, the old method of fetching the DT is used. > > [1] https://git.qemu.org/?p=SLOF.git;a=commitdiff;h=e6fc84652c9c00 > [2] https://git.qemu.org/?p=SLOF.git;a=commit;h=ecda95906930b80 > > Signed-off-by: Alexey Kardashevskiy <a...@ozlabs.ru>
Hrm. I've gotta say I'm not terribly convinced that it's worth adding
a new interface we'll need to maintain to save 8s on a somewhat
contrived testcase.
> ---
> arch/powerpc/kernel/prom_init.c | 43 +++++++++++++++++++++++++++++++++
> 1 file changed, 43 insertions(+)
>
> diff --git a/arch/powerpc/kernel/prom_init.c b/arch/powerpc/kernel/prom_init.c
> index f33ff4163a51..72e7a602b68e 100644
> --- a/arch/powerpc/kernel/prom_init.c
> +++ b/arch/powerpc/kernel/prom_init.c
> @@ -2457,6 +2457,48 @@ static void __init flatten_device_tree(void)
> prom_panic("Can't allocate initial device-tree chunk\n");
> mem_end = mem_start + room;
>
> + hdr = (void *) mem_start;
> + if (!call_prom_ret("fdt-fetch", 2, 1, NULL, mem_start,
> + room - sizeof(mem_reserve_map)) &&
> + hdr->version >= 17) {
> + u32 size;
> + struct mem_map_entry *fwrmap;
> +
> + /* Fixup the boot cpuid */
> + hdr->boot_cpuid_phys = cpu_to_be32(prom.cpu);
> +
> + /*
> + * Store the struct and strings addresses, mostly
> + * for consistency, only dt_header_start actually matters later.
> + */
> + dt_header_start = mem_start;
> + dt_string_start = mem_start + be32_to_cpu(hdr->off_dt_strings);
> + dt_string_end = dt_string_start +
> + be32_to_cpu(hdr->dt_strings_size);
> + dt_struct_start = mem_start + be32_to_cpu(hdr->off_dt_struct);
> + dt_struct_end = dt_struct_start +
> + be32_to_cpu(hdr->dt_struct_size);
> +
> + /*
> + * Calculate the reserved map location (which we put
> + * at the blob end) and update total size.
> + */
> + fwrmap = (void *)(mem_start + be32_to_cpu(hdr->off_mem_rsvmap));
> + hdr->off_mem_rsvmap = hdr->totalsize;
> + size = be32_to_cpu(hdr->totalsize);
> + hdr->totalsize = cpu_to_be32(size + sizeof(mem_reserve_map));
> +
> + /* Merge reserved map from firmware to ours */
> + for ( ; fwrmap->size; ++fwrmap)
> + reserve_mem(be64_to_cpu(fwrmap->base),
> + be64_to_cpu(fwrmap->size));
> +
> + rsvmap = (u64 *)(mem_start + size);
> +
> + prom_debug("Fetched DTB: %d bytes to @%lx\n", size, mem_start);
> + goto finalize_exit;
> + }
> +
> /* Get root of tree */
> root = call_prom("peer", 1, 1, (phandle)0);
> if (root == (phandle)0)
> @@ -2504,6 +2546,7 @@ static void __init flatten_device_tree(void)
> /* Version 16 is not backward compatible */
> hdr->last_comp_version = cpu_to_be32(0x10);
>
> +finalize_exit:
> /* Copy the reserve map in */
> memcpy(rsvmap, mem_reserve_map, sizeof(mem_reserve_map));
>
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
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