From b5318d302f8a20eacbbfc01b0ee35b108085a363 Mon Sep 17 00:00:00 2001 From: Andres Salomon Date: Mon, 29 Nov 2010 23:39:51 +0000 Subject: [PATCH] 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: Andres Salomon LKML-Reference: <20101129153951.74202a84@queued.net> Signed-off-by: H. Peter Anvin --- arch/x86/platform/olpc/olpc_dt.c | 28 +++++++++++++++++++++++----- 1 file changed, 23 insertions(+), 5 deletions(-) diff --git a/arch/x86/platform/olpc/olpc_dt.c b/arch/x86/platform/olpc/olpc_dt.c index 7054697..dab8746 100644 --- a/arch/x86/platform/olpc/olpc_dt.c +++ b/arch/x86/platform/olpc/olpc_dt.c @@ -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); - - prom_early_allocated += size; + if (free_mem < size) { + const size_t chunk_size = max(PAGE_SIZE, 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; } -- 2.7.4