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 hack, 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.) Signed-off-by: Andres Salomon <[email protected]> --- arch/x86/kernel/olpc_dt.c | 27 +++++++++++++++++++++++---- 1 files changed, 23 insertions(+), 4 deletions(-) diff --git a/arch/x86/kernel/olpc_dt.c b/arch/x86/kernel/olpc_dt.c index f660a11..44dd2ae 100644 --- a/arch/x86/kernel/olpc_dt.c +++ b/arch/x86/kernel/olpc_dt.c @@ -123,16 +123,35 @@ static int __init olpc_dt_pkg2path(phandle node, char *buf, } static unsigned int prom_early_allocated __initdata; +#define DT_CHUNK_SIZE (1<<12) 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); + if (free_mem >= size) { + /* allocate from the local cache */ + free_mem -= size; + res = mem; + mem += size; + return res; + } - prom_early_allocated += size; + /* + * To mimimize the number of allocations, grab 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 = alloc_bootmem(DT_CHUNK_SIZE); + if (res) { + prom_early_allocated += DT_CHUNK_SIZE; + memset(res, 0, DT_CHUNK_SIZE); + free_mem = DT_CHUNK_SIZE - size; + mem = res + size; + } return res; } -- 1.5.6.5 _______________________________________________ devicetree-discuss mailing list [email protected] https://lists.ozlabs.org/listinfo/devicetree-discuss
