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
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
/*
--
Chuck
"You can't read a newspaper if you can't read." --George W. Bush
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