Re: [PATCH kernel] RFC: prom_init: Fetch flatten device tree from the system firmware
From: David Gibson <hidden>
Date: 2017-10-16 06:11:25
On Mon, Oct 16, 2017 at 04:49:17PM +1100, Alexey Kardashevskiy wrote:
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". If "fdt-fetch" is not available, the old method is used. Signed-off-by: Alexey Kardashevskiy <redacted>
I like the concept, few details though..
quoted hunk ↗ jump to hunk
--- arch/powerpc/kernel/prom_init.c | 26 ++++++++++++++++++++++++++ 1 file changed, 26 insertions(+)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; + 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);
If SLOF is generating a tree it really should get this header field right as well.
+ /* 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));
.. and the reserve map for that matter. I don't really understand what you're doing here. Note also that the reserve map is required to be 8-byte aligned, which totalsize might not be.
quoted hunk ↗ jump to hunk
+ /* 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 + goto print_exit; + } + /* 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;
-- 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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