| Message ID | 20180315170859.93893-3-zsm@chromium.org (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Thu, Mar 15, 2018 at 05:08:58PM +0000, Zubin Mithra wrote: > Without CONFIG_THREAD_INFO_IN_TASK, core code maintains thread_info::cpu > and arch specific code can use this to build raw_smp_processor_id(). > With CONFIG_THREAD_INFO_IN_TASK, core code maintains task_struct::cpu, > and arch specific code cannot access this due to header file circular > dependency. > > Instead, we can maintain a percpu variable containing the cpu number. > > This also means that cpu numbers obtained using smp_processor_id cannot > be used to set_my_cpu_offset. Use task_cpu(current) instead to get the > cpu in those cases. > > Earlier raw_smp_processor_id() was current_thread_info()->cpu :- > mov r3, sp > bic r3, r3, #8128 > bic r3, r3, #63 > ldr r0, [r3, #16] > > Now it is *raw_cpu_ptr(&cpu_number) :- > movw r3, #57344 > movt r3, #32917 > mrc 15, 0, r0, cr13, cr0, {4} > ldr r0, [r3, r0] It's probably worth noting that with the thread_info moved off of the stack, were we to use that to get at the cpu number, this would require a similar sequence to the raw_cpu_ptr() code here. This might make more sense after a patch using a register for the thread_info (which would also allow for having separate IRQ stacks). > > Signed-off-by: Zubin Mithra <zsm@chromium.org> > --- > arch/arm/include/asm/cputype.h | 3 +++ > arch/arm/include/asm/smp.h | 3 ++- > arch/arm/kernel/setup.c | 2 +- > arch/arm/kernel/smp.c | 5 +++-- > arch/arm/kernel/topology.c | 5 +++++ > 5 files changed, 14 insertions(+), 4 deletions(-) > > diff --git a/arch/arm/include/asm/cputype.h b/arch/arm/include/asm/cputype.h > index cb546425da8a..10148c7af12f 100644 > --- a/arch/arm/include/asm/cputype.h > +++ b/arch/arm/include/asm/cputype.h > @@ -2,6 +2,9 @@ > #ifndef __ASM_ARM_CPUTYPE_H > #define __ASM_ARM_CPUTYPE_H > > +#include <asm/percpu.h> > +DECLARE_PER_CPU(int, cpu_number); > + Why isn't this defined in <asm/smp.h>, as we do on arm64? > --- a/arch/arm/include/asm/smp.h > +++ b/arch/arm/include/asm/smp.h > @@ -18,7 +18,8 @@ > # error "<asm/smp.h> included in non-SMP build" > #endif > > -#define raw_smp_processor_id() (current_thread_info()->cpu) > +#include <asm/cputype.h> > +#define raw_smp_processor_id() (*raw_cpu_ptr(&cpu_number)) It might be worth dragging the comment along from arm64, explaining why we must use *raw_cpu_ptr(), and not this_cpu_read(), etc. > --- a/arch/arm/kernel/topology.c > +++ b/arch/arm/kernel/topology.c > @@ -30,6 +30,9 @@ > #include <asm/cputype.h> > #include <asm/topology.h> > > +DEFINE_PER_CPU_READ_MOSTLY(int, cpu_number); > +EXPORT_PER_CPU_SYMBOL(cpu_number); Why not in smp.c, as with arm64? > + > /* > * cpu capacity scale management > */ > @@ -310,6 +313,8 @@ void __init init_cpu_topology(void) > for_each_possible_cpu(cpu) { > struct cputopo_arm *cpu_topo = &(cpu_topology[cpu]); > > + per_cpu(cpu_number, cpu) = cpu; Likewise, why isn't this in smp_prepare_cpus() in smp.c? This isn't toplogy related, so it would be better placed there. Thanks, Mark.
diff --git a/arch/arm/include/asm/cputype.h b/arch/arm/include/asm/cputype.h index cb546425da8a..10148c7af12f 100644 --- a/arch/arm/include/asm/cputype.h +++ b/arch/arm/include/asm/cputype.h @@ -2,6 +2,9 @@ #ifndef __ASM_ARM_CPUTYPE_H #define __ASM_ARM_CPUTYPE_H +#include <asm/percpu.h> +DECLARE_PER_CPU(int, cpu_number); + #include <linux/stringify.h> #include <linux/kernel.h> diff --git a/arch/arm/include/asm/smp.h b/arch/arm/include/asm/smp.h index 709a55989cb0..7e7b198174d6 100644 --- a/arch/arm/include/asm/smp.h +++ b/arch/arm/include/asm/smp.h @@ -18,7 +18,8 @@ # error "<asm/smp.h> included in non-SMP build" #endif -#define raw_smp_processor_id() (current_thread_info()->cpu) +#include <asm/cputype.h> +#define raw_smp_processor_id() (*raw_cpu_ptr(&cpu_number)) struct seq_file; diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c index fc40a2b40595..6323b4d80306 100644 --- a/arch/arm/kernel/setup.c +++ b/arch/arm/kernel/setup.c @@ -521,7 +521,7 @@ static void __init elf_hwcap_fixup(void) void notrace cpu_init(void) { #ifndef CONFIG_CPU_V7M - unsigned int cpu = smp_processor_id(); + unsigned int cpu = task_cpu(current); struct stack *stk = &stacks[cpu]; if (cpu >= NR_CPUS) { diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c index 2da087926ebe..9584a52eb156 100644 --- a/arch/arm/kernel/smp.c +++ b/arch/arm/kernel/smp.c @@ -372,7 +372,8 @@ asmlinkage void secondary_start_kernel(void) * All kernel threads share the same mm context; grab a * reference and switch to it. */ - cpu = smp_processor_id(); + cpu = task_cpu(current); + set_my_cpu_offset(per_cpu_offset(cpu)); mmgrab(mm); current->active_mm = mm; cpumask_set_cpu(cpu, mm_cpumask(mm)); @@ -436,7 +437,7 @@ void __init smp_cpus_done(unsigned int max_cpus) void __init smp_prepare_boot_cpu(void) { - set_my_cpu_offset(per_cpu_offset(smp_processor_id())); + set_my_cpu_offset(per_cpu_offset(task_cpu(current))); } void __init smp_prepare_cpus(unsigned int max_cpus) diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c index 24ac3cab411d..34b2136deab6 100644 --- a/arch/arm/kernel/topology.c +++ b/arch/arm/kernel/topology.c @@ -30,6 +30,9 @@ #include <asm/cputype.h> #include <asm/topology.h> +DEFINE_PER_CPU_READ_MOSTLY(int, cpu_number); +EXPORT_PER_CPU_SYMBOL(cpu_number); + /* * cpu capacity scale management */ @@ -310,6 +313,8 @@ void __init init_cpu_topology(void) for_each_possible_cpu(cpu) { struct cputopo_arm *cpu_topo = &(cpu_topology[cpu]); + per_cpu(cpu_number, cpu) = cpu; + cpu_topo->thread_id = -1; cpu_topo->core_id = -1; cpu_topo->socket_id = -1;
Without CONFIG_THREAD_INFO_IN_TASK, core code maintains thread_info::cpu and arch specific code can use this to build raw_smp_processor_id(). With CONFIG_THREAD_INFO_IN_TASK, core code maintains task_struct::cpu, and arch specific code cannot access this due to header file circular dependency. Instead, we can maintain a percpu variable containing the cpu number. This also means that cpu numbers obtained using smp_processor_id cannot be used to set_my_cpu_offset. Use task_cpu(current) instead to get the cpu in those cases. Earlier raw_smp_processor_id() was current_thread_info()->cpu :- mov r3, sp bic r3, r3, #8128 bic r3, r3, #63 ldr r0, [r3, #16] Now it is *raw_cpu_ptr(&cpu_number) :- movw r3, #57344 movt r3, #32917 mrc 15, 0, r0, cr13, cr0, {4} ldr r0, [r3, r0] Signed-off-by: Zubin Mithra <zsm@chromium.org> --- arch/arm/include/asm/cputype.h | 3 +++ arch/arm/include/asm/smp.h | 3 ++- arch/arm/kernel/setup.c | 2 +- arch/arm/kernel/smp.c | 5 +++-- arch/arm/kernel/topology.c | 5 +++++ 5 files changed, 14 insertions(+), 4 deletions(-)