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[PATCH] Add the vgetcpu vsyscall

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This patch adds a vgetcpu vsyscall, which depending on the CPU RDTSCP
capability uses either the RDTSCP or CPUID to obtain a CPU and node
numbers and pass them to the program.

AK: Lots of changes over Vojtech's original code:
Better prototype for vgetcpu()
It's better to pass the cpu / node numbers as separate arguments
to avoid mistakes when going from SMP to NUMA.
Also add a fast time stamp based cache using a user supplied
argument to speed things more up.
Use fast method from Chuck Ebbert to retrieve node/cpu from
GDT limit instead of CPUID
Made sure RDTSCP init is always executed after node is known.
Drop printk

Signed-off-by: Vojtech Pavlik <vojtech@suse.cz>
Signed-off-by: Andi Kleen <ak@suse.de>
This commit is contained in:
Vojtech Pavlik
2006-09-26 10:52:28 +02:00
committed by Andi Kleen
parent a670fad0ad
commit c08c820508
8 changed files with 130 additions and 14 deletions
Download Patch File Download Diff File Expand all files Collapse all files
arch/x86_64/kernel/vsyscall.c
+82 -2
View File
@@ -26,6 +26,7 @@
#include <linux/seqlock.h>
#include <linux/jiffies.h>
#include <linux/sysctl.h>
#include <linux/getcpu.h>
#include <asm/vsyscall.h>
#include <asm/pgtable.h>
@@ -33,11 +34,15 @@
#include <asm/fixmap.h>
#include <asm/errno.h>
#include <asm/io.h>
#include <asm/segment.h>
#include <asm/desc.h>
#include <asm/topology.h>
#define __vsyscall(nr) __attribute__ ((unused,__section__(".vsyscall_" #nr)))
int __sysctl_vsyscall __section_sysctl_vsyscall = 1;
seqlock_t __xtime_lock __section_xtime_lock = SEQLOCK_UNLOCKED;
int __vgetcpu_mode __section_vgetcpu_mode;
#include <asm/unistd.h>
@@ -127,9 +132,46 @@ time_t __vsyscall(1) vtime(time_t *t)
return __xtime.tv_sec;
}
long __vsyscall(2) venosys_0(void)
/* Fast way to get current CPU and node.
This helps to do per node and per CPU caches in user space.
The result is not guaranteed without CPU affinity, but usually
works out because the scheduler tries to keep a thread on the same
CPU.
tcache must point to a two element sized long array.
All arguments can be NULL. */
long __vsyscall(2)
vgetcpu(unsigned *cpu, unsigned *node, struct getcpu_cache *tcache)
{
return -ENOSYS;
unsigned int dummy, p;
unsigned long j = 0;
/* Fast cache - only recompute value once per jiffies and avoid
relatively costly rdtscp/cpuid otherwise.
This works because the scheduler usually keeps the process
on the same CPU and this syscall doesn't guarantee its
results anyways.
We do this here because otherwise user space would do it on
its own in a likely inferior way (no access to jiffies).
If you don't like it pass NULL. */
if (tcache && tcache->t0 == (j = __jiffies)) {
p = tcache->t1;
} else if (__vgetcpu_mode == VGETCPU_RDTSCP) {
/* Load per CPU data from RDTSCP */
rdtscp(dummy, dummy, p);
} else {
/* Load per CPU data from GDT */
asm("lsl %1,%0" : "=r" (p) : "r" (__PER_CPU_SEG));
}
if (tcache) {
tcache->t0 = j;
tcache->t1 = p;
}
if (cpu)
*cpu = p & 0xfff;
if (node)
*node = p >> 12;
return 0;
}
long __vsyscall(3) venosys_1(void)
@@ -200,6 +242,43 @@ static ctl_table kernel_root_table2[] = {
#endif
static void __cpuinit write_rdtscp_cb(void *info)
{
write_rdtscp_aux((unsigned long)info);
}
void __cpuinit vsyscall_set_cpu(int cpu)
{
unsigned long *d;
unsigned long node = 0;
#ifdef CONFIG_NUMA
node = cpu_to_node[cpu];
#endif
if (cpu_has(&cpu_data[cpu], X86_FEATURE_RDTSCP)) {
void *info = (void *)((node << 12) | cpu);
/* Can happen on preemptive kernel */
if (get_cpu() == cpu)
write_rdtscp_cb(info);
#ifdef CONFIG_SMP
else {
/* the notifier is unfortunately not executed on the
target CPU */
smp_call_function_single(cpu,write_rdtscp_cb,info,0,1);
}
#endif
put_cpu();
}
/* Store cpu number in limit so that it can be loaded quickly
in user space in vgetcpu.
12 bits for the CPU and 8 bits for the node. */
d = (unsigned long *)(cpu_gdt(cpu) + GDT_ENTRY_PER_CPU);
*d = 0x0f40000000000ULL;
*d |= cpu;
*d |= (node & 0xf) << 12;
*d |= (node >> 4) << 48;
}
static void __init map_vsyscall(void)
{
extern char __vsyscall_0;
@@ -214,6 +293,7 @@ static int __init vsyscall_init(void)
VSYSCALL_ADDR(__NR_vgettimeofday)));
BUG_ON((unsigned long) &vtime != VSYSCALL_ADDR(__NR_vtime));
BUG_ON((VSYSCALL_ADDR(0) != __fix_to_virt(VSYSCALL_FIRST_PAGE)));
BUG_ON((unsigned long) &vgetcpu != VSYSCALL_ADDR(__NR_vgetcpu));
map_vsyscall();
#ifdef CONFIG_SYSCTL
register_sysctl_table(kernel_root_table2, 0);