On Fri, 2006-06-23 at 09:53 -0400, Chuck Ebbert wrote:
> This is attempt #3 at vgetcpu() support for i386. It uses a GDT entry
> to hold cpu and node number for fast userspace access.
>
> changes since #2:
> added NUMA support (compile tested only, please test)
> speed improvement
> proper #define for GDT entry number
> general cleanup & documentation
>
I think a consistent interface like vgetcpu(*cpunum, *nodenum) will be
good across architectures. And then add the packagenum as well.
8bits per field seems okay but may run out of steam.
-rohit
> to-do:
> CFI annotations
>
> Test program:
>
> /* vgetcpu.c: test vgetcpu()
> * boot kernel with vgetcpu patch first, then build with:
> * gcc -O3 -o vgetcpu vgetcpu.c <srcpath>/arch/i386/kernel/vsyscall-int80.so
> * (don't forget the optimization (-O3))
> */
> #define _GNU_SOURCE
> #include <stdio.h>
> #include <stdlib.h>
>
> extern int __vgetcpu(void);
>
> #define rdtscll(t) asm("rdtsc" : "=A" (t))
>
> int main(int argc, char * const argv[])
> {
> long long tsc1, tsc2;
> int i, iters = 999999;
>
> i = __vgetcpu();
> printf("node: %d, cpu: %d\nBenchmarking...\n", i >> 8, i & 0xff);
>
> rdtscll(tsc1);
> for (i = 0; i < iters; i++)
> __vgetcpu();
> rdtscll(tsc2);
>
> printf("vgetcpu() took %llu clocks per call\n", (tsc2 - tsc1) / iters);
>
> return 0;
> }
>
> Signed-off-by: Chuck Ebbert <[email protected]>
>
> arch/i386/kernel/cpu/common.c | 3 +++
> arch/i386/kernel/head.S | 8 +++++++-
> arch/i386/kernel/smpboot.c | 2 ++
> arch/i386/kernel/vsyscall-getcpu.S | 26 ++++++++++++++++++++++++++
> arch/i386/kernel/vsyscall-int80.S | 2 ++
> arch/i386/kernel/vsyscall-sysenter.S | 2 ++
> arch/i386/kernel/vsyscall.lds.S | 1 +
> include/asm-i386/segment.h | 4 +++-
> 8 files changed, 46 insertions(+), 2 deletions(-)
>
> --- 2.6.17-32.orig/arch/i386/kernel/cpu/common.c
> +++ 2.6.17-32/arch/i386/kernel/cpu/common.c
> @@ -642,6 +642,9 @@ void __cpuinit cpu_init(void)
> ((((__u64)stk16_off) << 32) & 0xff00000000000000ULL) |
> (CPU_16BIT_STACK_SIZE - 1);
>
> + /* Set up GDT entry for per-cpu data */
> + gdt[GDT_ENTRY_VGETCPU].a |= cpu;
> +
> cpu_gdt_descr->size = GDT_SIZE - 1;
> cpu_gdt_descr->address = (unsigned long)gdt;
>
> --- 2.6.17-32.orig/arch/i386/kernel/head.S
> +++ 2.6.17-32/arch/i386/kernel/head.S
> @@ -525,7 +525,13 @@ ENTRY(cpu_gdt_table)
> .quad 0x004092000000ffff /* 0xc8 APM DS data */
>
> .quad 0x0000920000000000 /* 0xd0 - ESPFIX 16-bit SS */
> - .quad 0x0000000000000000 /* 0xd8 - unused */
> +
> + /*
> + * Use a GDT entry to store per-cpu data for user space (DPL 3.)
> + * 32-bit data segment, byte granularity, base 0, limit set at runtime.
> + */
> + .quad 0x0040f20000000000 /* 0xd8 - for per-cpu user data */
> +
> .quad 0x0000000000000000 /* 0xe0 - unused */
> .quad 0x0000000000000000 /* 0xe8 - unused */
> .quad 0x0000000000000000 /* 0xf0 - unused */
> --- /dev/null
> +++ 2.6.17-32/arch/i386/kernel/vsyscall-getcpu.S
> @@ -0,0 +1,26 @@
> +/*
> + * __vgetcpu()
> + *
> + * This file is #include'd by vsyscall-*.S to place vgetcpu after the
> + * sigreturn code.
> + *
> + * Returns logical CPU number in bits 0-7, node ID in bits 8-15;
> + * -EFAULT on error.
> + */
> +
> +#include <linux/errno.h>
> +#include <asm/segment.h>
> +
> + .text
> + .org __kernel_rt_sigreturn+32,0x90
> + .globl __vgetcpu
> + .type __vgetcpu,@function
> +__vgetcpu:
> +.LSTART_vgetcpu:
> + movl $((GDT_ENTRY_VGETCPU<<3)|3),%edx
> + movl $-EFAULT,%eax
> + lsll %edx,%eax
> + ret
> +.LEND_vgetcpu:
> + .size __vgetcpu,.-.LSTART_vgetcpu
> +
> --- 2.6.17-32.orig/arch/i386/kernel/vsyscall-int80.S
> +++ 2.6.17-32/arch/i386/kernel/vsyscall-int80.S
> @@ -51,3 +51,5 @@ __kernel_vsyscall:
> * Get the common code for the sigreturn entry points.
> */
> #include "vsyscall-sigreturn.S"
> +
> +#include "vsyscall-getcpu.S"
> --- 2.6.17-32.orig/arch/i386/kernel/vsyscall-sysenter.S
> +++ 2.6.17-32/arch/i386/kernel/vsyscall-sysenter.S
> @@ -120,3 +120,5 @@ SYSENTER_RETURN:
> * Get the common code for the sigreturn entry points.
> */
> #include "vsyscall-sigreturn.S"
> +
> +#include "vsyscall-getcpu.S"
> --- 2.6.17-32.orig/arch/i386/kernel/vsyscall.lds.S
> +++ 2.6.17-32/arch/i386/kernel/vsyscall.lds.S
> @@ -57,6 +57,7 @@ VERSION
> __kernel_vsyscall;
> __kernel_sigreturn;
> __kernel_rt_sigreturn;
> + __vgetcpu;
>
> local: *;
> };
> --- 2.6.17-32.orig/arch/i386/kernel/smpboot.c
> +++ 2.6.17-32/arch/i386/kernel/smpboot.c
> @@ -615,6 +615,7 @@ static inline void map_cpu_to_node(int c
> printk("Mapping cpu %d to node %d\n", cpu, node);
> cpu_set(cpu, node_2_cpu_mask[node]);
> cpu_2_node[cpu] = node;
> + get_cpu_gdt_table(cpu)[GDT_ENTRY_VGETCPU].a |= (node & 0xff) << 8;
> }
>
> /* undo a mapping between cpu and node. */
> @@ -626,6 +627,7 @@ static inline void unmap_cpu_to_node(int
> for (node = 0; node < MAX_NUMNODES; node ++)
> cpu_clear(cpu, node_2_cpu_mask[node]);
> cpu_2_node[cpu] = 0;
> + get_cpu_gdt_table(cpu)[GDT_ENTRY_VGETCPU].a &= ~(0xff << 8);
> }
> #else /* !CONFIG_NUMA */
>
> --- 2.6.17-32.orig/include/asm-i386/segment.h
> +++ 2.6.17-32/include/asm-i386/segment.h
> @@ -39,7 +39,7 @@
> * 25 - APM BIOS support
> *
> * 26 - ESPFIX small SS
> - * 27 - unused
> + * 27 - vgetcpu() data
> * 28 - unused
> * 29 - unused
> * 30 - unused
> @@ -74,6 +74,8 @@
> #define GDT_ENTRY_ESPFIX_SS (GDT_ENTRY_KERNEL_BASE + 14)
> #define __ESPFIX_SS (GDT_ENTRY_ESPFIX_SS * 8)
>
> +#define GDT_ENTRY_VGETCPU (GDT_ENTRY_KERNEL_BASE + 15)
> +
> #define GDT_ENTRY_DOUBLEFAULT_TSS 31
>
> /*
-
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