On Fri, Oct 22, 2010 at 05:22:47PM -0700, Andres Salomon wrote:
>
> 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)
PAGE_SIZE perhaps?
>
> 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;
> + }
These two hunks should be flipped around so that only one chunk does
the allocation from the pool. As so:
/*
* 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.
*/
if (free_mem < size) {
free_mem = max(DT_CHUNK_SIZE, size);
mem = alloc_bootmem(free_mem);
if (!mem) {
free_mem = 0;
return NULL;
}
memset(mem, 0, free_mem);
prom_early_allocated += free_mem;
}
res = mem;
free_mem -= size;
mem += size;
return res;
g.
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