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Commit b5318d30 authored by Andres Salomon's avatar Andres Salomon Committed by H. Peter Anvin
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x86, olpc: Speed up device tree creation during boot 



Calling alloc_bootmem() for tiny chunks of memory over and over is really
slow; on an XO-1, it caused the time between when the kernel started
booting and when the display came alive (post-lxfb probe) to increase
to 44s.  This patch optimizes the prom_early_alloc function by
calling alloc_bootmem for 4k-sized blocks of memory, and handing out
chunks of that to callers.  With this patch, the time between kernel load
and display initialization decreased to 23s.  If there's a better way to
do this early in the boot process, please let me know.

(Note: increasing the chunk size to 16k didn't noticably affect boot time,
and wasted 9k.)

v4: clarify comment, requested by hpa
v3: fix wasted memory buglet found by Milton Miller, and style fix.
v2: reorder prom_early_alloc as suggested by Grant.

Signed-off-by: default avatarAndres Salomon <dilinger@queued.net>
LKML-Reference: <20101129153951.74202a84@queued.net>
Signed-off-by: default avatarH. Peter Anvin <hpa@linux.intel.com>
parent c10d1e26

arch/x86/platform/olpc/olpc_dt.c

+23 −5
Original line number Diff line number Diff line
@@ -126,14 +126,32 @@ static unsigned int prom_early_allocated __initdata; 


void * __init prom_early_alloc(unsigned long size)

{

	static u8 *mem;

	static size_t free_mem;

	void *res;



	res = alloc_bootmem(size);

	if (res)

		memset(res, 0, size);

	if (free_mem < size) {

		const size_t chunk_size = max(PAGE_SIZE, size);



	prom_early_allocated += size;

		/*

		 * To mimimize the number of allocations, grab at least

		 * PAGE_SIZE of memory (that's an arbitrary choice that's

		 * fast enough on the platforms we care about while minimizing

		 * wasted bootmem) and hand off chunks of it to callers.

		 */

		res = alloc_bootmem(chunk_size);

		if (!res)

			return NULL;

		prom_early_allocated += chunk_size;

		memset(res, 0, chunk_size);

		free_mem = chunk_size;

		mem = res;

	}



	/* allocate from the local cache */

	free_mem -= size;

	res = mem;

	mem += size;

	return res;

}