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.) v2: reorder function as suggested by Grant. Signed-off-by: Andres Salomon <[email protected]> --- arch/x86/platform/olpc/olpc_dt.c | 27 ++++++++++++++++++++++----- 1 files changed, 22 insertions(+), 5 deletions(-) diff --git a/arch/x86/platform/olpc/olpc_dt.c b/arch/x86/platform/olpc/olpc_dt.c index b8c8ff9..0ab824d 100644 --- a/arch/x86/platform/olpc/olpc_dt.c +++ b/arch/x86/platform/olpc/olpc_dt.c @@ -126,14 +126,31 @@ static unsigned int prom_early_allocated __initdata; void * __init prom_early_alloc(unsigned long size) { + static u8 *mem = NULL; + static size_t free_mem = 0; 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 4k of + * memory (that's an arbitrary choice that matches PAGE_SIZE on + * the platforms we care about, and minimizes wasted bootmem) + * and hand off chunks of it to callers. + */ + res = mem = alloc_bootmem(chunk_size); + if (!res) + return NULL; + prom_early_allocated += chunk_size; + memset(res, 0, chunk_size); + free_mem = chunk_size; + } + /* allocate from the local cache */ + free_mem -= size; + res = mem; + mem += size; return res; } -- 1.7.2.3 _______________________________________________ devicetree-discuss mailing list [email protected] https://lists.ozlabs.org/listinfo/devicetree-discuss
