* Nathan Zimmer <nzimmer@xxxxxxx> wrote:
> The memory we set aside in the previous patch needs to be reinserted.
> We start this process via late_initcall so we will have multiple cpus to do
> the work.
>
> Signed-off-by: Mike Travis <travis@xxxxxxx>
> Signed-off-by: Nathan Zimmer <nzimmer@xxxxxxx>
> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
> Cc: Ingo Molnar <mingo@xxxxxxxxxx>
> Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
> Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
> Cc: Yinghai Lu <yinghai@xxxxxxxxxx>
> ---
> arch/x86/kernel/e820.c | 129 +++++++++++++++++++++++++++++++++++++++++++++++++
> drivers/base/memory.c | 83 +++++++++++++++++++++++++++++++
> include/linux/memory.h | 5 ++
> 3 files changed, 217 insertions(+)
>
> diff --git a/arch/x86/kernel/e820.c b/arch/x86/kernel/e820.c
> index 3752dc5..d31039d 100644
> --- a/arch/x86/kernel/e820.c
> +++ b/arch/x86/kernel/e820.c
> @@ -23,6 +23,7 @@
>
> #ifdef CONFIG_DELAY_MEM_INIT
> #include <linux/memory.h>
> +#include <linux/delay.h>
> #endif
>
> #include <asm/e820.h>
> @@ -397,6 +398,22 @@ static u64 min_region_size; /* min size of region to slice from */
> static u64 pre_region_size; /* multiply bsize for node low memory */
> static u64 post_region_size; /* multiply bsize for node high memory */
>
> +static unsigned long add_absent_work_start_time;
> +static unsigned long add_absent_work_stop_time;
> +static unsigned int add_absent_job_count;
> +static atomic_t add_absent_work_count;
> +
> +struct absent_work {
> + struct work_struct work;
> + struct absent_work *next;
> + atomic_t busy;
> + int cpu;
> + int node;
> + int index;
> +};
> +static DEFINE_PER_CPU(struct absent_work, absent_work);
> +static struct absent_work *first_absent_work;
That's 4.5 GB/sec initialization speed - that feels a bit slow and the
boot time effect should be felt on smaller 'a couple of gigabytes' desktop
boxes as well. Do we know exactly where the 2 hours of boot time on a 32
TB system is spent?
While you cannot profile the boot process (yet), you could try your
delayed patch and run a "perf record -g" call-graph profiling of the
late-time initialization routines. What does 'perf report' show?
Delayed initialization makes sense I guess because 32 TB is a lot of
memory - I'm just wondering whether there's some low hanging fruits left
in the mem init code, that code is certainly not optimized for
performance.
Plus with a struct page size of around 64 bytes (?) 32 TB of RAM has 512
GB of struct page arrays alone. Initializing those will take quite some
time as well - and I suspect they are allocated via zeroing them first. If
that memset() exists then getting rid of it might be a good move as well.
Yet another thing to consider would be to implement an initialization
speedup of 3 orders of magnitude: initialize on the large page (2MB)
grandularity and on-demand delay the initialization of the 4K granular
struct pages [but still allocating them] - which I suspect are a good
chunk of the overhead? That way we could initialize in 2MB steps and speed
up the 2 hours bootup of 32 TB of RAM to 14 seconds...
[ The cost would be one more branch in the buddy allocator, to detect
not-yet-initialized 2 MB chunks as we encounter them. Acceptable I
think. ]
Thanks,
Ingo
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