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SubjectRe: smp/swsusp done right
Date
Hi,

On Wednesday, 23 of March 2005 21:40, Pavel Machek wrote:
> Hi!
>
> This is against -mm kernel; it is smp swsusp done right, and it
> actually works for me. Unlike previous hacks, it uses cpu hotplug
> infrastructure. Disable CONFIG_MTRR before you try this...
>
> Test this if you can, and report any problems. If not enough people
> scream, this is going to -mm.
> Pavel
>
> --- clean-mm/drivers/pci/pci.c 2005-03-21 11:39:32.000000000 +0100
> +++ linux-mm/drivers/pci/pci.c 2005-03-22 01:41:48.000000000 +0100
> @@ -376,11 +376,13 @@
> if (!pci_find_capability(dev, PCI_CAP_ID_PM))
> return PCI_D0;
>
> +#if 0
> if (platform_pci_choose_state) {
> ret = platform_pci_choose_state(dev, state);
> if (ret >= 0)
> state = ret;
> }
> +#endif
> switch (state) {
> case 0: return PCI_D0;
> case 3: return PCI_D3hot;

You probably don't want the above change to go in the final patch?


> --- clean-mm/kernel/power/Kconfig 2005-01-22 21:24:53.000000000 +0100
> +++ linux-mm/kernel/power/Kconfig 2005-03-23 11:40:14.000000000 +0100
> @@ -28,7 +28,7 @@
>
> config SOFTWARE_SUSPEND
> bool "Software Suspend (EXPERIMENTAL)"
> - depends on EXPERIMENTAL && PM && SWAP
> + depends on EXPERIMENTAL && PM && SWAP && (HOTPLUG_CPU || !SMP)
> ---help---
> Enable the possibility of suspending the machine.
> It doesn't need APM.
> --- clean-mm/kernel/power/smp.c 2005-03-19 00:32:32.000000000 +0100
> +++ linux-mm/kernel/power/smp.c 2005-03-23 15:38:30.000000000 +0100
> @@ -7,79 +7,53 @@
> * This file is released under the GPLv2.
> */
>
> -#undef DEBUG
> -
> #include <linux/smp_lock.h>
> #include <linux/interrupt.h>
> #include <linux/suspend.h>
> #include <linux/module.h>
> #include <asm/atomic.h>
> #include <asm/tlbflush.h>
> +#include <asm/cpu.h>
>
> -static atomic_t cpu_counter, freeze;
> -
> -
> -static void smp_pause(void * data)
> -{
> - struct saved_context ctxt;
> - __save_processor_state(&ctxt);
> - printk("Sleeping in:\n");
> - dump_stack();
> - atomic_inc(&cpu_counter);
> - while (atomic_read(&freeze)) {
> - /* FIXME: restore takes place at random piece inside this.
> - This should probably be written in assembly, and
> - preserve general-purpose registers, too
> -
> - What about stack? We may need to move to new stack here.
> -
> - This should better be ran with interrupts disabled.
> - */
> - cpu_relax();
> - barrier();
> - }
> - atomic_dec(&cpu_counter);
> - __restore_processor_state(&ctxt);
> -}
> -
> -static cpumask_t oldmask;
> +cpumask_t frozen_cpus;
>
> void disable_nonboot_cpus(void)
> {
> - printk("Freezing CPUs (at %d)", smp_processor_id());
> - oldmask = current->cpus_allowed;
> - set_cpus_allowed(current, cpumask_of_cpu(0));
> - current->state = TASK_INTERRUPTIBLE;
> - schedule_timeout(HZ);
> - printk("...");
> - BUG_ON(smp_processor_id() != 0);
> -
> - /* FIXME: for this to work, all the CPUs must be running
> - * "idle" thread (or we deadlock). Is that guaranteed? */
> + int cpu, error;
>
> - atomic_set(&cpu_counter, 0);
> - atomic_set(&freeze, 1);
> - smp_call_function(smp_pause, NULL, 0, 0);
> - while (atomic_read(&cpu_counter) < (num_online_cpus() - 1)) {
> - cpu_relax();
> - barrier();
> + error = 0;
> + cpus_clear(frozen_cpus);
> + printk("Freezing cpus ...\n");
> + for_each_online_cpu(cpu) {
> + if (cpu == 0)
> + continue;
> + error = cpu_down(cpu);
> + if (!error) {
> + cpu_set(cpu, frozen_cpus);
> + printk("CPU%d is down\n", cpu);
> + continue;
> + }
> + printk("Error taking cpu %d down: %d\n", cpu, error);
> }
> - printk("ok\n");
> + BUG_ON(smp_processor_id() != 0);
> + if (error)
> + panic("cpus not sleeping");
> }

I'm not sure whether we should panic() here. It may be better to make
suspend fail and print a "please reboot immediately" message for the user.
In that case, the user may be able to reboot without loosing data ...


> void enable_nonboot_cpus(void)
> {
> - printk("Restarting CPUs");
> - atomic_set(&freeze, 0);
> - while (atomic_read(&cpu_counter)) {
> - cpu_relax();
> - barrier();
> - }
> - printk("...");
> - set_cpus_allowed(current, oldmask);
> - schedule();
> - printk("ok\n");
> + int cpu, error;
>
> + printk("Thawing cpus ...\n");
> + for_each_cpu_mask(cpu, frozen_cpus) {
> + if (cpu == 0)
> + continue;
> + error = cpu_up(cpu);
> + if (!error) {
> + printk("CPU%d is up\n", cpu);
> + continue;
> + }
> + printk("Error taking cpu %d up: %d\n", cpu, error);
> + panic("Not enough cpus");
> + }
> }
> -
> -
> --- clean-mm/kernel/power/swsusp.c 2005-03-21 11:39:33.000000000 +0100
> +++ linux-mm/kernel/power/swsusp.c 2005-03-23 15:34:53.000000000 +0100
> @@ -1194,8 +1194,11 @@
> return "version";
> if (strcmp(swsusp_info.uts.machine,system_utsname.machine))
> return "machine";
> +#if 0
> + /* We can't use number of CPUs when we use hotplug to remove them ;-))) */
> if(swsusp_info.cpus != num_online_cpus())
> return "number of cpus";
> +#endif
> return NULL;
> }
>
>
> --

I'll test it when I get the CPU hotplug on x86-64 done.

Greets,
Rafael


--
- Would you tell me, please, which way I ought to go from here?
- That depends a good deal on where you want to get to.
-- Lewis Carroll "Alice's Adventures in Wonderland"
-
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