Messages in this thread Patch in this message | | | Date | Mon, 30 Jan 2012 20:54:44 -0800 | From | Arjan van de Ven <> | Subject | smp: Start up non-boot CPUs asynchronously |
| |
From 3700e391ab2841a9f9241e4e31a6281aa59be5f1 Mon Sep 17 00:00:00 2001 From: Arjan van de Ven <arjan@linux.intel.com> Date: Mon, 30 Jan 2012 20:44:51 -0800 Subject: [PATCH] smp: Start up non-boot CPUs asynchronously
The starting of the "not first" CPUs actually takes a lot of boot time of the kernel... upto "minutes" on some of the bigger SGI boxes. Right now, this is a fully sequential operation with the rest of the kernel boot.
This patch turns this bringup of the other cpus into an asynchronous operation, saving significant kernel boot time (40% on my laptop!!). Basically now CPUs get brought up in parallel to disk enumeration, graphic mode bringup etc etc etc.
Note that the implementation in this patch still waits for all CPUs to be brought up before starting userspace; I would love to remove that restriction over time (technically that is simple), but that becomes then a change in behavior... I'd like to see more discussion on that being a good idea before I write that patch.
Second note: We add a small delay between the bring up of cpus, this is needed to actually get a boot time improvement. If we bring up CPUs straight back-to-back, we hog the cpu hotplug lock for write, and that lock is used everywhere during initialization for read. By adding a small delay, we allow those tasks to make progress.
CC: Milton Miller <miltonm@bga.com> CC: Andrew Morton <akpm@linux-foundation.org> CC: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Arjan van de Ven <arjan@linux.intel.com> --- kernel/smp.c | 32 +++++++++++++++++++++++++++++++- 1 files changed, 31 insertions(+), 1 deletions(-)
diff --git a/kernel/smp.c b/kernel/smp.c index db197d6..b83d82e 100644 --- a/kernel/smp.c +++ b/kernel/smp.c @@ -12,6 +12,8 @@ #include <linux/gfp.h> #include <linux/smp.h> #include <linux/cpu.h> +#include <linux/async.h> +#include <linux/delay.h> #ifdef CONFIG_USE_GENERIC_SMP_HELPERS static struct { @@ -664,17 +666,45 @@ void __init setup_nr_cpu_ids(void) nr_cpu_ids = find_last_bit(cpumask_bits(cpu_possible_mask),NR_CPUS) + 1; } +void __init async_cpu_up(void *data, async_cookie_t cookie) +{ + unsigned long nr = (unsigned long) data; + /* + * we can only up one cpu at a time, due to the hotplug lock; + * it's better to wait for all earlier CPUs to be done before + * us so that the bring up order is predictable. + */ + async_synchronize_cookie(cookie); + /* + * wait a little bit of time between cpus, to allow + * the kernel boot to not get stuck for a long time + * on the hotplug lock. We wait longer for the first + * CPU since many of the early kernel init code is + * of the hotplug-lock using type. + */ + if (nr < 2) + msleep(100); + else + msleep(5); + cpu_up(nr); +} + /* Called by boot processor to activate the rest. */ void __init smp_init(void) { unsigned int cpu; /* FIXME: This should be done in userspace --RR */ + + /* + * But until we do this in userspace, we're going to do this + * in parallel to the rest of the kernel boot up.-- Arjan + */ for_each_present_cpu(cpu) { if (num_online_cpus() >= setup_max_cpus) break; if (!cpu_online(cpu)) - cpu_up(cpu); + async_schedule(async_cpu_up, (void *) cpu); } /* Any cleanup work */ -- 1.7.6.4
-- Arjan van de Ven Intel Open Source Technology Centre For development, discussion and tips for power savings, visit http://www.lesswatts.org
| |