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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] arm: don't use atomic operations to gate non-boot CPUs
On Thu, 2012-03-15 at 14:15 +0000, Tim Deegan wrote:
> # HG changeset patch
> # User Tim Deegan <tim@xxxxxxx>
> # Date 1331820837 0
> # Node ID 6f52e5de1b942432ffa6c3b8d194e5e2771c1957
> # Parent 4da1453ed61c28a366162b49b2f59f62e070a799
> arm: don't use atomic operations to gate non-boot CPUs.
>
> Since the cache is not enabled that early, better not to rely on
> load-linked/store-conditional. Instead, have the boot CPU call the
> other CPUs by their IDs, just like we do later for proper CPU bringup.
>
> Signed-off-by: Tim Deegan <tim@xxxxxxx>
Committed, thanks.
(do we care about trailing whitespace? there was some, "git am" warns
me...)
>
> diff -r 4da1453ed61c -r 6f52e5de1b94 xen/arch/arm/head.S
> --- a/xen/arch/arm/head.S Thu Mar 15 11:47:27 2012 +0000
> +++ b/xen/arch/arm/head.S Thu Mar 15 14:13:57 2012 +0000
> @@ -71,16 +71,13 @@ start:
> bics r12, r0, #(0xff << 24) /* Mask out flags to get CPU ID */
> beq boot_cpu /* If we're CPU 0, boot now */
>
> - /* Non-boot CPUs wait here to be woken up one at a time.
> - * This is basically an open-coded spin-lock to serialize. */
> - ldr r0, =boot_gate /* VA of gate */
> + /* Non-boot CPUs wait here to be woken up one at a time. */
> +1: wfe
> + dsb
> + ldr r0, =smp_up_cpu /* VA of gate */
> add r0, r0, r10 /* PA of gate */
> - mov r1, #1 /* (1 == locked) */
> -1: wfe
> - ldrex r2, [r0] /* Linked read of current value */
> - teq r2, #0 /* (0 == unlocked) */
> - strexeq r2, r1, [r0] /* Matching update -> locked */
> - teq r2, #0 /* (0 == succeeded) */
> + ldr r1, [r0] /* Which CPU is being booted? */
> + teq r1, r12 /* Is it us? */
> bne 1b
>
> boot_cpu:
> @@ -270,16 +267,7 @@ paging:
> teq r12, #0
> beq launch
>
> - /* Signal the next non-boot CPU to come and join us here */
> - ldr r0, =boot_gate /* VA of gate */
> - add r0, r0, r10 /* PA of gate */
> - mov r1, #0 /* (0 == unlocked) */
> - str r1, [r0]
> - dsb
> - isb
> - sev
> -
> - /* Move on to the relocated pagetables */
> + /* Non-boot CPUs need to move on to the relocated pagetables */
> mov r0, #0
> ldr r4, =boot_httbr /* VA of HTTBR value stashed by CPU 0 */
> add r4, r4, r10 /* PA of it */
> diff -r 4da1453ed61c -r 6f52e5de1b94 xen/arch/arm/setup.c
> --- a/xen/arch/arm/setup.c Thu Mar 15 11:47:27 2012 +0000
> +++ b/xen/arch/arm/setup.c Thu Mar 15 14:13:57 2012 +0000
> @@ -38,11 +38,6 @@
> #include <asm/setup.h>
> #include "gic.h"
>
> -/* Spinlock for serializing CPU bringup */
> -unsigned long __initdata boot_gate = 1;
> -/* Number of non-boot CPUs ready to enter C */
> -unsigned long __initdata ready_cpus = 0;
> -
> static __attribute_used__ void init_done(void)
> {
> free_init_memory();
> @@ -152,8 +147,6 @@ void __init start_xen(unsigned long boot
> void *fdt;
> size_t fdt_size;
> int cpus, i;
> - paddr_t gate_pa;
> - unsigned long *gate;
>
> fdt = (void *)BOOT_MISC_VIRT_START
> + (atag_paddr & ((1 << SECOND_SHIFT) - 1));
> @@ -169,25 +162,11 @@ void __init start_xen(unsigned long boot
> console_init_preirq();
> #endif
>
> + cpus = gic_init();
> + make_cpus_ready(cpus, boot_phys_offset);
> +
> percpu_init_areas();
> set_processor_id(0); /* needed early, for smp_processor_id() */
> -
> - cpus = gic_init();
> -
> - printk("Waiting for %i other CPUs to be ready\n", cpus - 1);
> - /* Bring the other CPUs up to paging before the original
> - * copy of .text gets overwritten. We need to use the unrelocated
> - * copy of boot_gate as that's the one the others can see. */
> - gate_pa = ((unsigned long) &boot_gate) + boot_phys_offset;
> - gate = map_domain_page(gate_pa >> PAGE_SHIFT) + (gate_pa & ~PAGE_MASK);
> - *gate = 0;
> - unmap_domain_page(gate);
> - /* Now send an event to wake the first non-boot CPU */
> - asm volatile("dsb; isb; sev");
> - /* And wait for them all to be ready. */
> - while ( ready_cpus + 1 < cpus )
> - smp_rmb();
> -
> __set_current((struct vcpu *)0xfffff000); /* debug sanity */
> idle_vcpu[0] = current;
>
> diff -r 4da1453ed61c -r 6f52e5de1b94 xen/arch/arm/smpboot.c
> --- a/xen/arch/arm/smpboot.c Thu Mar 15 11:47:27 2012 +0000
> +++ b/xen/arch/arm/smpboot.c Thu Mar 15 14:13:57 2012 +0000
> @@ -19,6 +19,7 @@
> #include <xen/cpu.h>
> #include <xen/cpumask.h>
> #include <xen/delay.h>
> +#include <xen/domain_page.h>
> #include <xen/errno.h>
> #include <xen/init.h>
> #include <xen/mm.h>
> @@ -41,11 +42,17 @@ static unsigned char __initdata cpu0_boo
> /* Pointer to the stack, used by head.S when entering C */
> unsigned char *init_stack = cpu0_boot_stack;
>
> +/* Shared state for coordinating CPU bringup */
> +unsigned long smp_up_cpu = 0;
> +static bool_t cpu_is_dead = 0;
> +
> +/* Number of non-boot CPUs ready to enter C */
> +unsigned long __initdata ready_cpus = 0;
> +
> void __init
> smp_prepare_cpus (unsigned int max_cpus)
> {
> int i;
> - set_processor_id(0); /* needed early, for smp_processor_id() */
>
> cpumask_clear(&cpu_online_map);
> cpumask_set_cpu(0, &cpu_online_map);
> @@ -56,9 +63,30 @@ smp_prepare_cpus (unsigned int max_cpus)
> cpumask_copy(&cpu_present_map, &cpu_possible_map);
> }
>
> -/* Shared state for coordinating CPU bringup */
> -unsigned long smp_up_cpu = 0;
> -static bool_t cpu_is_dead = 0;
> +void __init
> +make_cpus_ready(unsigned int max_cpus, unsigned long boot_phys_offset)
> +{
> + unsigned long *gate;
> + paddr_t gate_pa;
> + int i;
> +
> + printk("Waiting for %i other CPUs to be ready\n", max_cpus - 1);
> + /* We use the unrelocated copy of smp_up_cpu as that's the one the
> + * others can see. */
> + gate_pa = ((paddr_t) (unsigned long) &smp_up_cpu) + boot_phys_offset;
> + gate = map_domain_page(gate_pa >> PAGE_SHIFT) + (gate_pa & ~PAGE_MASK);
> + for ( i = 1; i < max_cpus; i++ )
> + {
> + /* Tell the next CPU to get ready */
> + /* TODO: handle boards where CPUIDs are not contiguous */
> + *gate = i;
> + asm volatile("dsb; isb; sev");
> + /* And wait for it to respond */
> + while ( ready_cpus < i )
> + smp_rmb();
> + }
> + unmap_domain_page(gate);
> +}
>
> /* Boot the current CPU */
> void __cpuinit start_secondary(unsigned long boot_phys_offset,
> diff -r 4da1453ed61c -r 6f52e5de1b94 xen/include/asm-arm/smp.h
> --- a/xen/include/asm-arm/smp.h Thu Mar 15 11:47:27 2012 +0000
> +++ b/xen/include/asm-arm/smp.h Thu Mar 15 14:13:57 2012 +0000
> @@ -16,6 +16,12 @@ DECLARE_PER_CPU(cpumask_var_t, cpu_core_
>
> extern void stop_cpu(void);
>
> +/* Bring the non-boot CPUs up to paging and ready to enter C.
> + * Must be called after Xen is relocated but before the original copy of
> + * .text gets overwritten. */
> +extern void
> +make_cpus_ready(unsigned int max_cpus, unsigned long boot_phys_offset);
> +
> #endif
> /*
> * Local variables:
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